A Survey of XML Tree Patterns <s> Tree patterns in algebraic frameworks <s> XML data are expected to be widely used in Web information systems and EC/EDI applications. Such applications usually use a large number of XML data. First, we must allow users to retrieve only necessary portions of XML data by specifying search conditions to flexibly describe such applications. Second, we must allow users to combine XML data from different sources. To this end, we will provide a query language for XML data tentatively called XQL. We have designed XQL, keeping in mind its continuity with database standards such as SQL and OQL although we don't stick to its strict conformity. In this paper, we describe the requirements for a query language for XML data and explain the functionality of XQL including XML version of database operators such as select, joint, sort, grouping, union, and view definition. We make brief comments on the implementation and semantics. <s> BIB001 </s> A Survey of XML Tree Patterns <s> Tree patterns in algebraic frameworks <s> The World Wide Web promises to transform human society by making virtually all types of information instantly available everywhere. Two prerequisites for this promise to be realized are a universal markup language and a universal query language. The power and flexibility of XML make it the leading candidate for a universal markup language. XML provides a way to label information from diverse data sources including structured and semi-structured documents, relational databases, and object repositories. Several XML-based query languages have been proposed, each oriented toward a specific category of information. Quilt is a new proposal that attempts to unify concepts from several of these query languages, resulting in a new language that exploits the full versatility of XML. The name Quilt suggests both the way in which features from several languages were assembled to make a new query language, and the way in which Quilt queries can combine information from diverse data sources into a query result with a new structure of its own. <s> BIB002 </s> A Survey of XML Tree Patterns <s> Tree patterns in algebraic frameworks <s> With the recent and rapid advance of the Internet, management of structured documents such as XML documents and their databases has become more and more important. A number of query languages for XML documents have been proposed up to the present. Some of them enable tag-based powerful document structure manipulation. However, their contents processing capability is very limited. Here, the contents processing implies the similarity-based selection, ranking, summary generation, topic extraction, and so on, as well as simple string-based pattern matching. In this paper, we propose an extensible XML query language X2QL, which features inclusion of user-defined foreign functions to process document contents in the context of XML-QL-based document structure manipulation. This feature makes it possible to integrate application-oriented high-level contents processing facilities into querying documents. We also describe an implementation of an X2QL query processing systemon top of XSLT processors. <s> BIB003
The first XML algebras have appeared in 1999  ,  in conjunction with efforts aiming to define a powerful XML query language BIB002 ,  , BIB001 ,  , BIB003 . Note that they have appeared before the first specification of XQuery, the now standard XML query language, which was issued in 2001  . The aim of an XML tree algebra is to feature a set of operators to manipulate and query data trees. Query results are also data trees.