A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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 present the reality of interest <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 present the reality of interest <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 present the reality of interest <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 present the reality of interest <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> BIB005 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB006 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB007 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB008 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB009 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB010 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB011 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB012 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB013 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB014 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB015 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB016 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB017 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB018 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB019 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB020 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB021 </s> A Survey on Visual Query Systems in the Web Era (extended version) <s> Visual representation adopted to present the reality of interest <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> BIB022
This feature has been borrowed from the work of Catarci BIB001 . The reality of interest is modeled by a designer by means of a data metamodel as, for example, the entity/relationship metamodel or a graph data metamodel. As a result of the modelization process, a data model is obtained and it is presented to the user so that (s)he formulates queries on it. The ways the data model is presented to the user are: The category in which each selected paper falls as well as a more detailed explanation of some of the papers are given in Section 3. Diagram-based Data metamodels come with an associated typical representation for their elements. For example, in the entity/relationship metamodel, there are many representations available and one of them consists of drawing rectangles for the entity types, diamonds for the relationship types and ovals for the attributes. In the diagram-based option, the user has available a diagrammatical representation of the data model elaborated with the typical graphical representation for the elements of the metamodel. Icon-based Unlike the diagram-based approach, in this representation there are only iconic representations of some elements of the data model, but the user does not have available the complete data model. According to Catarci BIB001 , 'these VQS are mainly addressed to users who are not familiar with the concepts of data models and may find it difficult to interpret even an E-R diagram'. The aim of the icons is to represent a certain concept by means of its metaphorical power. The problem of these systems is how to construct them in such a way that they express a meaning which is understandable without ambiguity to the users. In column 2 of Table 2 and Table 3 , we summarise the options of the VQSs for specifying the database. Diagram-based The queries in the Conquer-II query language BIB002 are written in a conceptual schema based on the ORM conceptual modeling approach. In ORM, the world is modelled in terms of objects and roles and the notion of attribute is not used. Paper BIB003 deals with heterogeneous databases. It provides a formally defined and semantically rich data model, the Graph Model. A conceptually single database, the Graph Model Database, is built for the different heterogeneous databases and the user formulates his/her queries against this model. Paper BIB004 adopts the EER model to present the reality of interest. It presents the MiTRA system, composed of several modules. One of them, the Schema Visualization System, extracts database schema information and presents the visual structure on the user's screen in the form of an EER schema in the schema visualisation window, which is always available. Paper BIB005 proposes the EPISQUE interface, where the epistemic diagrams represents the real world in terms of entities, events and states. It has the idea that ER diagrams do not provide enough information so that people outside the organization can form SQL queries against the database. So, the E/R diagrams are extended to epistemic diagrams. In BIB007 , the model of the real world is called vision. A vision is composed of visual concepts and associations between them and is a clear representation of a relational database. Several visions may be built on the same database, to deal with different kinds of users. An example of a vision can be seen in Figure 1 . It is a combination of the diagram and of the icon approaches. The data model in Hyperlog of BIB008 is called the Hypernode Model. The schema of the database is a set of hypernode types, which may be recursively defined. An example of schema in Hyperlog can be seen in Figure 2 . Paper BIB012 presents XQBE, a tool for querying XML data. The XML schema or DTD specification is offered to the user as a starting point for specifying queries in a navigational way. In paper BIB011 the XML structure is visualized as a GUI tree on the left part of the SchemaBrowser. There, nodes can be activated and can serve as a basis for automatically generating a query tree. An example of a library schema is shown in Figure 3 . In paper BIB013 the data model consists of classes and their attributes as well as associations between classes. In the interface, there are three canvases and In BIB016 , an interface for ordered XQuery, called IFOX, is described. In this approach, the schema is visually presented as a tree, where the elements, the attributes and the terminal elements are clearly distinguished. The XML schema is specified by the user or is built by a schema constructor. In paper BIB019 , the database schema is specified as a unified conceptual graph. For example, the student table is represented as in Figure 4 . In BIB020 , queries are expressed on data warehouse schemas composed of tables. A typical schema consists of a fact table and several dimension tables related with the fact table. This type of structure is commonly known as a star schema. Paper BIB021 presents VMQL, a language for querying models used in large scale model based development. VMQL uses the respective modeling language of the source model as the query language. So, if the source model is written in UML, the queries are also written using UML. In Figure 5 , we can see an example for data, in this case, a UML class diagram. Paper BIB022 offers an interface divided into two parts. In the left part, a diagram of an XML document is shown to represent source XML documents, lets users explore the documents, and selects parts of the documents to be used in queries. Icon-based Paper BIB006 shows classes and extents. For a class, the only visible information is its icon and its name. In BIB009 the queries are built on the relational model. Queries are built on the Vis table, which is a logical view of a relation in the database and may be a join of more than one physical table. The attributes of this table are available as icons in the interface for building the iconic queries. Paper BIB010 presents a Temporal Visual Query Environment(TVQE) for historical databases. In this environment, the data model is called Temporal Graph Model(TGM) and has a set of Temporal Graphical Primitives(TGPs). The schema includes classes, attributes, relationships between classes, temporal classes, temporal attributes and temporal relationships. The database schema adopts an iconic representation which exploits a graphical notebook metaphor. Form-based Paper BIB017 presents the schema in a form-based manner. The user drags the fields of a query into shelves. Polaris interacts with multidimensional relational databases in the form of spreadsheets or available inside the DBMS. Faceted In paper BIB018 , the data are modeled as faceted classifications which organizes a set of items into multiple, independent taxonomies. Each classification is known as facet and the collection of classification data is faceted metadata. The specific category labels within a facet are facet values. For example, the set of items can be architectural works. For these items, the facets are the architect, the location or the materials. The facet values for materials are stone, steel, etc. Unknown The VISUAL system of  is a query language intended for handling scientific experiment data. It offers a textual representation of the object-oriented data model on which the query system is built. The data model includes classes as Frame or Particle. In paper  , the schema is not directly presented to the user. Basically, the user specifies the beginning and the end of the query and CQL uses built-in metaknowledge about the application schema to find the complete path. For expert users, the interface has the option of seeing the complete database application diagram. This is a semantically constrained entity-relationship diagram which includes entity types and associations among themselves. Paper BIB015 proposes the MiMi system, a deep integration of several protein interaction databases. The entire dataset and metadata were stored in Timber, a native XML database but it is not clear how the schema is made available to the users. Paper BIB014 deals with web query languages but does not offer a schema since semistructured data typically comes without a fixed schema.