A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Visual query systems (VQSs) are query systems for databases that use visual representations to depict the domain of interest and express related requests. VQSs can be seen as an evolution of query languages adopted into database management systems; they are designed to improve the effectiveness of the human?computer communication. Thus, their most important features are those that determine the nature of the human?computer dialogue. In order to survey and compare existing VQSs used for querying traditional databases, we first introduce a classification based on such features, namely the adopted visual representations and the interaction strategies. We then identify several user types and match the VQS classes against them, in order to understand which kind of system may be suitable for each kind of user. We also report usability experiments which support our claims. Finally, some of the most important open problems in the VQS area are described. <s> BIB001 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Formulating non-trivial queries in relational languages such as SQL and QBE can prove daunting to end users. ConQuer is a conceptual query language that allows users to formulate queries naturally in terms of elementary relationships. operators such as and, of', snot' and maybe contextual forclauses and object-correlation, thus avoiding the need to deal explicitly with implementation details such as relational tables, null values. outer joins, group-by clauses and correlated subqueries. While most conceptual query languages are based on the Entity-Relationship approach, ConQuer is based on Object-Role Modeling (ORM), which exposes semantic domains as conceptual object types. allowing queries to be formulated via paths through the information space. As a result of experience with the first implementation of ConQuer, the language has been substantially revised and extended to become ConQuer-II. and a new tool, ActiveQuery, has been developed with an improved interface. ConQuer-II's new features such as arbitrary correlation and subtyping enable it to be used for a wide range of advanced conceptual queries. <s> BIB002 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> During the past few years our research efforts have been inspired by two different needs. On one hand, the number of non-expert users accessing databases is growing apace. On the other, information systems will no longer be characterized by a single centralized architecture, but rather by several heterogeneous component systems. In order to address such needs we have designed a new query system with both user-oriented and multidatabase features. The system's main components are an adaptive visual interface, providing the user with different and interchangeable interaction modalities, and a “translation layer”, which creates and offers to the user the illusion of a single homogeneous schema out of several heterogeneous components. Both components are founded on a common ground, i.e. a formally defined and semantically rich data model, the Graph Model, and a minimal set of Graphical Primitives, in terms of which general query operations may be visually expressed. The Graph Model has a visual syntax, so that graphical operations can be applied on its components without unnecessary mappings, and an object-based semantics. The aim of this paper is twofold. We first present an overall view of the system architecture and then give a comprehensive description of the lower part of the system itself. In particular, we show how schemata expressed in different data models can be translated in terms of Graph Model, possibly by exploiting reverse engineering techniques. Moreover, we show how mappings can be established between well-known query languages and the Graphical Primitives. Finally, we describe in detail how queries expressed by using the Graphical Primitives can be translated in terms of relational expressions so to be processed by actual DBMSs. <s> BIB003 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Resolving different levels of heterogeneity present in heterogeneous database environments is a subject that has been addressed in a number of research projects. Graphical user interfaces are becoming the de-facto form of user interface in many application areas, including database management systems. The use of a popular visualisation notation to present schemas at an abstract level and to permit direct user manipulation of this visualisation in formulating queries is one of the most widespread approaches to providing database graphical user interfaces. The existence of a variety of visualisation notations (which are in common use to visualise schemas) introduces additional heterogeneity to a distributed system, in visual representation at the end-user interface level. This paper describes the use of meta-programming techniques which are applied to resolve this visual model heterogeneity on existing databases, by allowing a user to select a preferred visualisation notation, both to view the schema and to query the database. <s> BIB004 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> The WWW has a great potential of evolving into a globally distributed digital document library. The primary use of such a library is to retrieve information quickly and easily. Because of the size of these libraries, simple keyword searches often result in too many matches. More complex searches involving boolean expressions are difficult to formulate and understand. This paper describes QBT (Query By Templates), a visual method for formulating queries for structured document databases modeled with SGML. Based on Zloof's QBE (Query By Example), this method incorporates the structure of the documents for composing powerful queries. The goal of this technique is to design an interface for querying structured documents without prior knowledge of the internal structure. This paper describes the rationale behind QBT, illustrates the query formulation principles using QBT, and describes results obtained from a usability analysis on a prototype implementation of QBT on the Web using the Java/sup TM/ programming language. <s> BIB005 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Database users without sufficient understanding of database schemas are normally daunted by the task of query formulation. To alleviate these concerns, we have come up with a visual query system that allows users to express queries at the conceptual level. This interface works by representing a targeted database schema at the conceptual level and allows the user to enter restriction, projection and join conditions in an interactive fashion. The mapping between the conceptual level and the relational schema of a targeted database is accomplished via the usage of the knowledge representation language Lk. We have built a prototype that works with human genome databases. <s> BIB006 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> In this paper we describe Kaleidoquery, a visual query language for object databases with the same expressive power as OQL. We will describe the design philosophy behind the filter flow nature of Kaleidoquery and present each of the language's constructs, giving examples and relating them to OQL. The Kaleidoquery language is described independent of any implementation details, but a brief description of a 3D interface currently under construction for Kaleidoquery is presented. The queries in this implementation of the language are translated into OQL and then passed to the object database O2 for evaluation. <s> BIB007 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Abstract The adoption of a visual interface can simplify the query formulation process in DBMSs by enabling naive users to interact with a friendly environment. In this work, we propose a visual query language based on a diagrammatic paradigm, used for both data and query representation. The external data model is called vision and is made up of the visual primitives of concept and association. The external query model is based on the definition of a viewpoint, which is a perspective for accessing data defined dynamically by selecting a concept of primary interest. Internally, the data model is relational and the query language is SQL. An intermediate graph-based model ensures consistent mapping between the visual and the relational worlds. Our language has been implemented within a tool which can be mounted on top of any relational DBMS supporting ODBC. The system has been tested with naive users; the results of the experiment are reported and compared with those obtained with other visual languages. <s> BIB008 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> The Web is explored by many users, but only a few of them have experience in using query languages. Thus, one of the greatest challenges, provided by XML, is to create a query language simple enough for the naive user. In this paper, we present EquiX|a powerful and easy to use query language for XML. The main goal in designing EquiX is to strike the right balance between expressive power and simplicity. EquiX has a form-based GUI that is constructed automatically from the DTDs of XML documents. Query forms are built from well known HTML primitives. The result of a query in EquiX is a collection of XML documents, and it is automatically generated from the query without explicit speci cation of the format of the result. Knowledge of XML syntax is not required in order to use EquiX. Yet, EquiX is able to express rather complicated queries, containing quanti cation, negation and aggregation. We present the data model in Section 2. In Sections 3, and 4 we introduce the query language syntax, and semantics. Automatic generation of query results is discussed in Section 6. In Section 7, we review related work and conclude. <s> BIB009 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Hyperlog is a declarative, graph based language that supports database querying and update. It visualizes schema information, data, and query output as sets of nested graphs, which can be stored, browsed, and queried in a uniform way. Thus, the user need only be familiar with a very small set of syntactic constructs. Hyperlog queries consist of a set of graphs that are matched against the database. Database updates are supported by means of programs consisting of a set of rules. The paper discusses the formulation, evaluation, expressiveness, and optimization of Hyperlog queries and programs. We also describe a prototype implementation of the language and we compare and contrast our approach with work in a number of related areas, including visual database languages, graph based data models, database update languages, and production rule systems. <s> BIB010 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Abstract The Delaunay system supports a visual language that is specifically geared to the querying and visualization of databases. In this paper, we concentrate on the information visualization capabilities of the system. A distinctive feature of Delaunay is its full personalization capabilities: users can define their visualizations from scratch without limiting themselves to pre-defined visualization modes. Fine customization of the visualization is achieved by the availability of a visual alphabet of atomic graphical symbols and by the expressive power of the visual query language, which supports recursion. We describe the key components of the Delaunay system, namely its interface modules, which support advanced visualization techniques and principles, and its efficient constraint solver. The successful implementation of Delaunay demonstrates the feasibility of a powerful database system with which users can effectively specify a wide variety of visualizations supporting data and visualization exploration for different kinds of applications including graph visualization and business analysis. <s> BIB011 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Recent database applications are typically oriented towards a large set of non-expert users, and therefore, they need to be equipped with suitable interfaces facilitating the interaction with the system. Moreover, the incorporation of the time dimension in database systems is a desirable feature. Indeed, several temporal data models and the corresponding textual query languages have been proposed. However, there is a limited amount of research concerning the investigation of user-oriented languages for querying temporal databases. Our proposal addresses such a need. In particular, we propose a visual query environment, namely Temporal Visual Query Environment (TVQE) which provides an easier interaction of the user with temporal databases. The system adopts a diagrammatic representation of the database schema (including temporal classes and relationships) and a "graphical notebook" as interaction metaphor. In our approach, non-database experts are released from syntactical difficulties which are typical of textual languages, and they can easily express temporal queries by means of elementary graphical operations (e.g. click on a node label). Differently from many proposals in the field of visual query languages, the language underlying TVQE is provided with formal syntax and semantics. It is based on a minimal set of temporal graphical primitives (TGPs), which are defined on a Temporal Graph Model (TGM), with visual syntax and object-based semantics. In this paper we mainly concentrate on the formal aspects of TVQE, and provide some hints on the visual interaction mechanisms and implementation issues. <s> BIB012 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> In this paper a visual approach to querying in large spatial databases is presented. A diagrammatic technique utilising a data flow metaphor is used to express different kinds of spatial and non-spatial constraints. Basic filters are designed to represent the various types of queries in such systems. Icons for different types of spatial relations are used to denote the filters. Different granularities of the relations are presented in a hierarchical fashion when selecting the spatial constraints. Spatial joins and composite spatial and non-spatial constraints are represented consistently in the language. <s> BIB013 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Abstract We report on an iconic interface that implements a restricted subset of SQL commands for querying a database. Database queries and the query language's tokens (verbs, adjectives, etc.) are represented by icons. To construct a query, the user composes structured iconic expressions according to the grammar of the iconic language. The language and grammar include rules for iconic construction (Quadral Composite Icons and Serial Composite Icons). In brief, the user visually queries the database by issuing structured iconic queries composed in a systematic manner. The paper describes the syntactic and semantic principles behind structured iconic expressions and the way that these principles have been implemented in an iconic interface. User evaluation is informally reported, and the role of metaphor in the design and interpretation of icons is discussed. <s> BIB014 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> QURSED enables the development of web-based query forms and reports (QFRs) that query and report semistructured XML data, i.e., data that are characterized by nesting, irregularities and structural variance. The query aspects of a QFR are captured by its query set specification, which formally encodes multiple parameterized condition fragments and can describe large numbers of queries. The run-time component of QURSED produces XQuery-compliant queries by synthesizing fragments from the query set specification that have been activated during the interaction of the end-user with the QFR. The design-time component of QURSED, called QURSED Editor, semi-automates the development of the query set specification and its association with the visual components of the QFR by translating visual actions into appropriate query set specifications. We describe QURSED and illustrate how it accommodates the intricacies that the semistructured nature of the underlying database introduces. We specifically focus on the formal model of the query set specification, its generation via the QURSED Editor and its coupling with the visual aspects of the web-based form and report. <s> BIB015 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> With the advent of XML as a format for data ex-change and semistructured databases, query languagesfor XML and semistructured data have become in-creasingly popular.Many such query languages, like XPath andXQuery, are navigational in the sense that their vari-able binding paradigm requires the programmer tospecify path navigations through the document (ordata item). In contrast, some other languages – suchas UnQL [1] and Xcerpt [2] – are pattern-based: theirvariable binding paradigm is that of mathematical log-ics, i.e. the programmer speciﬁes patterns (or terms)including variables. Arguably, a pattern-based vari-able binding paradigm makes complex queries mucheasier to specify and to read, thus improving theprogramming eﬃciency. Sustaining this ﬁrst claimwith practical examples is one of the objectives of thepresent demonstration.Xcerpt [2] is an experimental pattern-based queryand transformation language for XML and semistruc-tured data. Xcerpt uses patterns both for bindingvariables in query expressions and for reassembling thevariables (bound to data items in query expressions) inso-called construct terms. Arguably, a pattern-baseddocument construction combined with a pattern-basedvariable binding results in a rather intuitive, userfriendly, and programming eﬃcient language. Sustain-ing this second claim is another objective of the presentdemonstration.Xcerpt is experimental in the sense that its purposeis to investigate and test another, non-navigational ap-proach to retrieve data from the Web than that ofthe widespread query languages XPath and XQuery.Nonetheless, Xcerpt has been prototypically imple- <s> BIB016 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> We introduce FoXQ, a visual language that enables end users to query XML We are currently developing a language that brings a lot of the functionality of XQuery within the reach of the end users without getting them embroiled in the intricacies of XQuery syntax. The query interface is form-based and the query model is based on a document metaphor in which the users formulate queries by filling out forms. <s> BIB017 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Abstract We present a visual language for querying and transforming XML data. The language is based on a visual document metaphor and the notion of document patterns and rules. It combines a dynamic form-based interface for defining queries and transformation rules with powerful pattern matching capabilities and offers thus a highly expressive visual language. The design of the visual language is specifically targeted at end users. <s> BIB018 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> This article reports on the XML retrieval system x2 that has been developed at the University of Munich over the last 5 years. In a typical session with x2, the user first browses a structural summary of the XML database in order to select interesting elements and keywords occurring in documents. Using this intermediate result, queries combining structure and textual references are composed semiautomatically. After query evaluation, the full set of answers is presented in a visual and structured way. x2 largely exploits the structure found in documents, queries and answers to enable new interactive visualization and exploration techniques that support mixed IR and database-oriented querying, thus bridging the gap between these three views on the data to be retrieved. Another salient characteristic of x2 that distinguishes it from other visual query systems for XML is that it supports various degrees of detailedness in the presentation of answers, as well as techniques for dynamically reordering, grouping and ranking retrieved elements once the complete answer set has been computed. <s> BIB019 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> The spreading of XML data in many contexts of modern computing infrastructures and systems causes a pressing need for adequate XML querying capabilities; to address this need, the W3C is proposing XQuery as the standard query language for XML, with a language paradigm and a syntactic flavor comparable to the SQL relational language. XQuery is designed for meeting the requirements of skilled database programmers; its inherent complexity makes the new language unsuited to unskilled users.In this article we present XQBE (XQuery By Example), a visual query language for expressing a large subset of XQuery in a visual form. In designing XQBE, we targeted both unskilled users and expert users wishing to speed up the construction of their queries; we have been inspired by QBE, a relational language initially proposed as an alternative to SQL, which is supported by Microsoft Access. QBE is extremely successful among users who are not computer professionals and do not understand the subtleties of query languages, as well as among professionals who can draft their queries very quickly.According to the hierarchical nature of XML, XQBE's main graphical elements are trees. One or more trees denote the documents assumed as query input, and one tree denotes the document produced by the query. Similar to QBE, trees are annotated so as to express selection predicates, joins, and the passing of information from the input trees to the output tree.This article formally defines the syntax and semantics of XQBE, provides a large set of examples, and presents a prototype implementation. <s> BIB020 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> This paper introduces SEEQ - a System for Enhanced Exploration and Querying. It is a visual query system for databases that uses a diagrammatic visualization for most user interaction. The database schema is displayed as a graph of the data model including classes, associations and attributes. The user formulates the query in terms of direct manipulation as a graph of the schema objects, additional operators and constants. The output of the query is visualized as a graph of instances and constants or in some other format that is appropriate for the data. SEEQ can operate on arbitrary relational data base provided that the schema is in XML format. <s> BIB021 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> In this poster we discuss a graphical notation for representing queries for semistructured data. We try to strike a balance between expressiveness of the query language and simplicity and understandability of the graphical notation. We present the primitives of the notation by means of examples. <s> BIB022 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Database researchers have striven to improve the capability of a database in terms of both performance and functionality. We assert that the usability of a database is as important as its capability. In this paper, we study why database systems today are so difficult to use. We identify a set of five pain points and propose a research agenda to address these. In particular, we introduce a presentation data model and recommend direct data manipulation with a schema later approach. We also stress the importance of provenance and of consistency across presentation models. <s> BIB023 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> In contrast to a traditional setting where users express queries against the database schema, we assert that the semantics of data can often be understood by viewing the data in the context of the user interface (UI) of the software tool used to enter the data. That is, we believe that users will understand the data in a database by seeing the labels, drop-down menus, tool tips, or other help text that are built into the user interface. Our goal is to allow domain experts with little technical skill to understand and query data. In this paper, we present our GUi As View (Guava) framework and describe how we use forms-based UIs to generate a conceptual model that represents the information in the user interface. We then describe how we generate a query interface from the conceptual model. We characterize the resulting query language using a subset of the relational algebra. Since most application developers want to craft a physical database to meet desired performance needs, we present here a transformation channel that can be configured by instantiating one or more of our transformation operators. The channel, once configured, automatically transforms queries from our query interface into queries that address the underlying physical database and delivers query results that conform to our query interface. In this paper, we define and formalize our database transformation operators. The contributions of this paper are that first, we demonstrate the feasibility of creating a query interface based directly on the user interface and second, we introduce a general purpose database transformation channel that will likely shorten the application development process and increase the quality of the software by automatically generating software artifacts that are often made manually and are prone to errors. <s> BIB024 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Even though XQuery has become a standard for querying semi-structured data, its syntax is too complex for occasional users. This paper describes a user friendly interface called IFOX (Interface For Ordered XQuery) that enables non experienced users to build easily complex XQueries. To that end, we use an algebraic-like representation to build XQueries. This representation is based on the XAlgebra described in [17]. Moreover, many applications require answers to queries to be order sensitive. For example, in a biomedical application where a set of genes is stored in a XML file, the order in the output when querying these data is crucial. With issue in mind, we propose a normalization process which not only preserves order in answers to queries but also enables optimization techniques. <s> BIB025 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> During the last decade, multidimensional databases have become common in the business and scientific worlds. Analysis places significant demands on the interfaces to these databases. It must be possible for analysts to easily and incrementally change both the data and their views of it as they cycle between hypothesis and experimentation. In this paper, we address these demands by presenting the Polaris formalism, a visual query language for precisely describing a wide range of table-based graphical presentations of data. This language compiles into both the queries and drawing commands necessary to generate the visualization, enabling us to design systems that closely integrate analysis and visualization. Using the Polaris formalism, we have built an interactive interface for exploring multidimensional databases that analysts can use to rapidly and incrementally build an expressive range of views of their data as they engage in a cycle of visual analysis. <s> BIB026 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Faceted metadata and navigation have become major topics in library science, information retrieval and Human-Computer Interaction (HCI). This work surveys a range of extant approaches in this design space, classifying systems along several relevant dimensions. We use that survey to analyze the organization of data and its querying within faceted browsing systems. We contribute formal entity-relationship (ER) and relational data models that explain that organization and relational query models that explain systems' browsing functionality. We use these types of models since they are widely used to conceptualize data and to model back-end data stores. Their structured nature also suggests ways in which both the models and faceted systems might be extended. <s> BIB027 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> MashQL, a novel query formulation language for querying and mashing up structured data on the Web, doesn't require users to know the queried data's structure or the data itself to adhere to a schema. In this article, the authors address the fact that being a language, not merely an interface (and simultaneously schema-free), MashQL faces a particular set of challenges. In particular, the authors propose and evaluate a novel technique for optimizing queries over large data sets to allow instant user interaction. <s> BIB028 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Querying databases is a common daily task carried out by a great deal of end-users who do not have specific skills in SQL language. Today, most of the database interaction is achieved by means of query interfaces provided by the database environment. However, most of these interfaces suffer from expressive limitations, since they are mostly based on metaphors that drastically restrict the expressiveness of the SQL language that is generated and executed in the background. In this paper, we present a visual interaction language and tool focused on easily querying databases by end-users. We make no assumption on the level of the user's experience with query languages, as our visual metaphor is intended for querying databases by unskilled end-users and also leveraging the restriction on the expressiveness of the queries created by them. We also report on some late braking results obtained by an experiment carried out with real users. <s> BIB029 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> Given a graph database D and a query graph g, an exact subgraph matching query asks for the set S of graphs in D that contain g as a subgraph. This type of queries find important applications in several domains such as bioinformatics and chemoinformatics, where users are generally not familiar with complex graph query languages. Consequently, user-friendly visual interfaces which support query graph construction can reduce the burden of data retrieval for these users. Existing techniques for subgraph matching queries built on top of such visual framework are designed to optimize the time required in retrieving the result set S from D, assuming that the whole query graph has been constructed. This leads to sub-optimal system response time as the query processing is initiated only after the user has finished drawing the query graph. In this paper, we take the first step towards exploring a novel graph query processing paradigm, where instead of processing a query graph after its construction, it interleaves visual query construction and processing to improve system response time. To realize this, we present an algorithm called G BLENDER that prunes false results and prefetches partial query results by exploiting the latency offered by the visual query formulation. It employs a novel action-aware indexing scheme that exploits users' interaction characteristics with visual interfaces to support efficient retrieval. Extensive experiments on both real and synthetic datasets demonstrate the effectiveness and efficiency of our solution. <s> BIB030 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> The basic idea of using Conceptual Graphs as interface to relational databases has been stated by Sowa. The full expressiveness of modern database query languages includes negation and the so-called aggregating functions too. These features were introduced in [1] by means of Nested Concept Graphs with Cuts. The novelty of the paper relies in the specific design of the relation between tables by means of a software named CGDBInterface, which can connect to an existing database by giving the type and the name of the database, a login name and password. The software then displays the structure of the database in form of a conceptual graph. The software provides a graph editor to assist the user in constructing a query with Nested Concept Graphs. To the best of our knowledge, such a software was not developed yet. <s> BIB031 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> In large scale model based development, analysis level models are more like knowledge bases than engineering artifacts. Their effectiveness depends, to a large degree, on the ability of domain experts to retrieve information from them ad-hoc. For large scale models, however, existing query facilities are inadequate. The visual model query language (VMQL) is a novel approach that uses the respective modeling language of the source model as the query language, too. The semantics of VMQL is defined formally based on graphs, so that query execution can be defined as graph matching. VMQL has been applied to several visual modeling languages, implemented, and validated in small case studies, and several controlled experiments. <s> BIB032 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to express the queries <s> XML is the standard way of representing and storing rapidly-growing semi-structured data on the Internet. While XQuery has been proposed by W3C as the standard query language for XML data, the complexity of the language is the major overhead for users to express the queries and for software to process the queries efficiently. Considering mobile devices are more popular than desktop computers, expressing and/or processing XQuery becomes even more cumbersome on mobile devices. This paper proposes a visual XQuery specification language called VXQ. By intuitive abstractions of XML and XQuery, the proposed system can generate XQuery queries for users with little knowledge about XML and the language. The proposed visual language is easier to use and more expressive than previous proposals, and is also suitable for mobile devices where typing is not desired. Furthermore, we extend our proposed visual XQuery to support query rewriting and optimization for multiple XQuery systems. Experiments show that, in practice, our query rewriting reduces the query execution time significantly. <s> BIB033
This feature has been borrowed from the work of Catarci BIB001 and we have adapted it to the object of the survey by adding the Faceted value. The list of values is: Next, we describe briefly the values of this feature. Diagram-based The diagram-based option means that the query is expressed on a diagrammatic representation of the data model. In column 3 of Table 2 and Table 3 , we summarise the options of the VQSs for formulating the query. Diagram-based Conquer-II queries BIB002 are mapped into SQL queries for execution in commercial DBMS. The queries are shown in textual form as a tree of predicates connecting objects. For example, a query like 'each academic as well as their degrees (if any) that are worth more than a 5 rating' is expressed as shown in Figure 6 . The user specifies a query by dragging to the query pane an object type from an object pick list. Then, another pane displays the roles played by that object and the user selects the appropriate ones. In this way, users specify queries without knowing the underlying structure. For specifying queries in the Graph Database Model of BIB003 , two graphical primitive are defined: selection of nodes and drawing of edge. The primitives are used to express any query-oriented interaction with the database. For example, the query 'retrieve the names of all the students whose age is greater than 21 and living in NY' is expressed graphically as shown in Figure 7 . The queries in MiTRA BIB004 are expressed on an EER schema. For doing so, the Graphical Query System allows users to manipulate the EER schema. It presents the available graphical query operators to the user, allowing the formulation of queries involving selection, projection, join and recursion. For example, the query 'Find the names of all students taught by R. SMITH.' is specified as shown in Figure 8 . In EPISQUE BIB006 , the user creates queries in several steps. First, (s)he places restriction, projection and join on epistemic diagrams. Next, they are converted into SQL expressions and finally they are sent to the targeted db for processing. For the specification of queries in VISIONARY of BIB008 , the notion of viewpoint is used. The expressive power of VISIONARY is limited to restricted join queries enriched with aggregation functions. The visual queries are translated into SQL and then to the DBMS. Basically, a viewpoint is a primary concept of the vision together with several associations starting from the primary concept. The formulation of a query consists of the following steps: (1) choose a primary concept, (2) edit the viewpoint, (3) choose attributes to be retrieved, (4) formulate selections on attributes and (5) order and/or group the results. Paper BIB010 presents Hyperlog, a declarative, graph-based language that supports database querying. A Hyperlog query consists of a number of graphs which are matched against the hypernodes in the database and which generate graphical output. The query 'suppliers who do not supply Widge2' is specified in Hyperlog as in Figure 9 . Hyperlog admits the negation, conjunction, and disjunction of queries. Builtin functions and relational operators can be visualized as hypernodes, and intentional information can be derived by encapsulating programs within templates. In X2 BIB019 , the user selects nodes of interest in the XML diagram and the system automatically generates query trees from the nodes selected. An example can be seen in Figure 10 where the query 'I would like to see interesting recent papers on XML written by Sally Sonntag' is shown. In SEEQ BIB021 queries are depicted in the query canvas. They can contain operators, constants and sub-queries. For example, the query 'find the students whose last name begins with 'B' and who have more than 60 credits' is depicted in Figure 11 . Paper BIB028 proposes a query-by-diagram language called MashQL. With this language, people query the web by building data mashups diagramatically. The paper assumes that web data sources are represented in RDF, and SPARQL is the query language to which the graphical mashup is translated. The novelty of MashQL is that it allows querying a data source without any prior understanding of the schema or the structure of the source. The specification of mashups is as follows: After a user selects the dataset in the RDF input module, the user selects the query subject in a drop-down list generated from the dataset. To add a restriction on the chosen object, a list of possible properties is dynamically generated. For the selected properties, user may then choose an object filter. The query 'retrieve Hackers articles published after 2000 from two web locations' expressed with MashQL is shown in Figure 12 . VISQUE BIB029 presents as a main feature the possibility of new queries such as union, intersection, in and not in, not covered in other papers but there are also other complex query operations not covered in the paper. I have not found any specific example in this paper. GBLENDER BIB030 proposes the problem of finding those graphs of a graph database which contains a query graph. The user formulates a query by clickingand-dragging items on the query canvas. In Figure 13 we can see the formulation of a query but the paper does not offer the corresponding textual version. VXQ BIB033 offers an interface divided into two parts. In the right part, the user composes queries by exploring the diagram of the XML document displayed on the left pane of the prototype. For example, the query 'create a flat list of all title-author pairs with the year of publication for all books published by AddisonWesley after 1991, and present these books in reverse chronological order by years and then in alphabetical order by titles for each year' is specified as can be seen in Figure 14 . Icon-based In the VISUAL system of  , queries are implemented as objects and interact with each other for query processing. An example of a query is 'find the particles each of which has a size equal to 3 microns and resides in the set of frames named StressFractureFrames' (see its graphical representation in Paper BIB007 presents the graphical query language Kaleidoquery, whose target language is OQL. Both languages have the same expressive power. The queries follow the filter flow model. The input are class instances and their information is filtered by constraints placed on the attributes of the class. For example, Figure 16 (a) represents the query 'find the people whose age is less than 20 and whose name is Smith'. The instances from the input extent flow through the query and are filtered through the two constraints. The query 'find the name of the companies which have at least one employee who earns more than 25000 euros and is older than 60' is represented in Figure 16(b) . The Delaunay query language interface BIB011 supports standard SQL clauses including select, from and where. The queries are specified on a class and the way of working is that the user arranges graphical objects that specify how to visualize objects of the class. The complete specification of a visual query is called DOODLE program. In Figure 17 , we can see a DOODLE program which specifies a bar chart visualization. In paper BIB012 , the queries are specified on the notebook, which visualizes schemas. The approach is hybrid because it is a combination of diagrammatic and iconic representation. The query condition is specified by means of dialog boxes, which contain menus, spin boxes and sliders for specifying temporal constants, predicates on time instants or predicates on time periods. For example, the query 'which salaries did the employees earn when they changed their level for the last time' is represented in this system as in Figure 18 , where we can see several selected and displayed nodes in the query. Paper BIB013 concentrates on specifying queries for Geographical Information Systems. Query diagrams are constructed using filters, represented by icons, between data input and output elements. The filter indicates the type of constraint expressed. Two types of join operations are possible: nonspatial joins and spatial joins, the latter are expressions of spatial relationships between spatial objects. In Figure 19 we can see the query 'find all the motorway roads that cross counties with population more than 50000' In paper BIB014 , the SQL sentences include only SELECT, FROM, WHERE and ORDER BY clauses. Queries are specified in a Query Assembly Frame, which consists of two subframes: the Query Header Frame (QHF) and the Selection/ Search Criteria Frame (SCF). The QHF accommodates the SELECT verb and its attributes as a composite icon. The SCF receives and accommodates sequences of icons representing the Selection/Search criteria. For example the query 'find the name, age and monthly salary of employees whose age is less than a particular value and has a particular skill. Order the result by age' is expressed as in Figure 20 . The language visXcerpt BIB016 uses a pattern-based approach to query XML data. It is well suited for visual language because the patterns are two dimensional structures that conceptually are very close to two dimensional visual representations. An example of a query in visXcerpt is 'select product elements having an origin with vendor attribute Sanchez or origin with vendor attribute DeRuiter'. Its graphical representation can be seen in Figure 21 . Paper BIB020 presents the XQBE visual query language for expressing a large set of XQuery in a visual form. The schema-driven editing mode allows the user to build a query by means of a construction guided by available XML schema or DTD specifications. The user draws the queries by choosing the graphical constructs from the toolbar. For example, the XQBE query 'list books published by Addison-Wesley after 1991, including their year and title' can be seen in Figure 22 . The paper BIB022 deals with the graphical representation of queries over semistructured data on the web represented as RDF, a W3C standard. They define a facet, which can be seen as a filter condition over an RDF graph and offer a graphical representation of it. For example, in Figure 23 we can see the query 'get resources that Andreas Harth knows' In BIB025 , an interface for ordered XQuery, called IFOX, is presented. The queries are represented as trees where the leaves are XSource operators, the internal nodes are XOperators such as XJoin or XUnion and the root node is the XOperator XConstruct. For example, the query 'For each book found in http://localhost/bib.xml whose price is below 70 and where the book is also found in http://localhost/review.xml, list the title of the book and its price from each source' is expressed in IFOX as shown in Figure 24 . The query includes the operators XSource, Xjoin, XRestrict and XConstruct. In CGBDI BIB031 , the queries are specified also as a simple conceptual graph. For example, the query 'select for every student group, the average of student's cgpa, if the average is greater than or equal to 8.5' is represented as in Figure 25 Queries in VMQL BIB032 are drawn by using a palette of icons which offers the icons of the source metamodel. So, there appears icons like Class, Package or Generalization. The query can be seen in Figure 26 . In GMQL  , queries attempt to find information from multimedia databases. They have chosen a reduced but meaningful set of symbols to express queries. An example can be seen in Figure 27 where, the movies satisfying that: (1) the poster of each one of these movies contains three inner image objects: two 'HORSE' and one 'SUN'; or (2) the poster of each one of these movies contains two inner image objects: one 'PERSON' and one 'DOG' are found. Form-based Paper BIB005 generalizes QBE for databases containing complex structured data. A QBT interface displays a template and the user issues a query by entering ex-amples of what (s)he is searching for in the template. In BIB009 the Equix system is presented. A query form is created in HTML from the DTD of the underlying database. Intuitively, the user creates an example of the document (s)he is searching for. Paper BIB015 presents QURSED which is a visual query system generator rather than only a visual query system. The Editor takes as input an XML Schema and generates an interface for the development of web-based query forms and reports (QFRs). An example can be seen in Figure 28 . FoXQ BIB017 , based on BIB018 , presents a system that helps users build queries on XML documents incrementally by navigating through layers of forms. Next, the queries are translated into XQuery. For example, the query 'return a list of all the titles in a bibliography database' is expressed as in Figure 29 . With the aid of users, in paper  a form-based interface for querying databases was developed (see Figure 30 ). This interface followed well-established guidelines on the design of human interfaces. It has four clearly distinguished zones: targets or information you want to know, sources or information you have available, semantic relationships and select conditions. Paper BIB023 proposes up to five interfaces to query the MiMI system. One of them is the forms interface, from which the authors discuss the pros and cons. The main pro is that it does not require knowledge of query language for novice users. The main con is that the limited number of queries available in the interface might 'dissatisfy many users'. Paper BIB024 presents the GUi As View (Guava) framework for generating query interfaces from user interfaces for domain experts with little technical skills to understand query data. The rationale behind this is as follows: The interface for data capturing is typically designes to be easy to use by domain experts. However, if they want to query data, there are two options: (a) have someone write a special query interface or (b) use SQL to express queries against the database schema. The proposal of the paper is to follow option (a) but the query interface is generated automatically from the user interface by the Guava framework. The approach of Guava is equivalent in expressive power to singlestatement conjunctive queries where joins are restricted to foreign keys and selection can use any of the six comparators to relate a column against a constant, but not a column against another column. In Polaris BIB026 , the user specifies a query by means of a table, which consists of a number of rows, columns, and layers. In the rows and columns of the table, the user specifies fields of the database as well as data aggregations. Each table entry, or pane, contains a set of records, built from these data, that are visually encoded as a set of marks to create a graphic. For example, a query for showing sales versus profit for different product types in different quarters can be seen in Figure 31 . The user has specifed in the vertical axis the product type and the total of sales for the product. In the horizontal axis, the user has specified the quarter and the total profit of the sales. Faceted Paper BIB027 presents faceted user interfaces, which operate on faceted metadata by letting users select one or more values from any number of facets. The advantage for users is that the user interface can present only valid selections, but this simplification also has drawbacks: the expressivity is sacrificed by only allowing certain classes of queries, for example, only conjunctive conditions. An example of a faceted interface is Flamenco (see Figure 32) where the items are Nobel Prizes. 