D. Maier. Database Desiderata for an XML Query Language, 1998. http://www.w3.org/TandS/QL/QL98/pp/maier.html.  Home/Search   Document Not in Database   Summary   Related Articles   Check

.... t Title Author a Author Book Bib IN books.xml , y 1991 CONSTRUCT a Figure 5 1: XMLQL Query Operation Selection and Extraction 49 The different operations that have to be supported by an XML query language are selection, extraction, reduction, restructuring and combination [25]. These terms are explained below with queries to indicate the operations performed. 5.2.1 Selection and Extraction Selection is the process of choosing a document element based on content, structure or attributes. Extraction is the process of pulling out particular elements of a document. Select ....

D. Maier, "Database desiderata for an XML Query Language," In Proceedings of the Query Languages workshop QL'98, Cambridge, Mass., Dec. 1998

....such as XPath [2] is convenient because it provides with regular expressions such as , and wildcards that give rise to a flexible node retrieval. Query and transformation languages developed since the mid 90es for XML [2] and semistructured data e.g. XQuery [2] the precursors of XQuery [3], and XSLT [2] rely upon such a path oriented selection. They use patterns (also called templates) for expressing how the selected data, expressed by paths, are re arranged (or re constructed) into new data items. Thus, such languages intertwine construct parts, i.e. the construction patterns, and ....

....and other query languages, queries might have several answers, each answer binding the query variables differently. Symmetry. Queries should allow similar forms of incomplete specifications in breadth, i.e. concerning siblings, and in depth, i.e. concerning children. Note that the requirements of [3] are fulfilled by or compatible with the basic query language defined below. Below, the following pairwise disjoint sets of symbols are referred to: A set 2; of identifiers, a set 2 of labels (or tags or strings) a set 1 of label variables, a set ] t of term (or data item) variables. ....

Maier, D.: Database Desiderata for an XML Query Language. In: Proceedings of QL'98 - The Query Languages Workshop. (1998) http://www.w3.org/TandS/qL/qL98/.

....natural and results in simple programs. For more complex queries, especially for queries involving several variables, the navigational approach often leads to intricate programs. Furthermore, the intertwining of construction and query parts in languages such as XQuery and most of its precursors [9] arguably often yields programs that are di#cult to read and hence to use and to maintain. Also, the possibility to specify forward and reverse axes in path languages like XPath might further increase the complexity of query programs, while the intuitive meaning is often not complicated at ....

Maier, D.: Database Desiderata for an XML Query Language. In: Proc. of QL'98 - The Query Languages Workshop. (1998)

....within the World Wide Web Consortium and within many academic institutions and Internet related companies. Some proposals and comparisons of query languages for XML are presented in a number of papers (e.g. 3, 8] A list of desired characteristics of XML query languages was proposed by Maier [12]. For such languages, query engines allowing users to effectively process the data stored in XML repositories are crucial to exploiting the full power of XML. Two streams of activities can be observed: in one stream, new semistructured data models and query languages are proposed [1, 4, 5, 7, 9, ....

....of the Answer query. Note that the body of a rule can be empty. 4. XML SQL expressions use cases In this section, we present example queries that illustrate ten essential features of XML SQL language. We will use running example from [2. We refer our discussion to desiderata proposed by Maier [ 12], as well to those discussed in [8,5, 3] 4.1. Selecting and extracting Our first example, Query 1 in Section 2, selects all books published by Addison Wesley after 1991, and extracts them to construct a new XML document. Given a document and a query on the document, the document selection is ....

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Maier D., Database desiderata for an XML query language, Proc. of the Query Languages Workshop, Cambridge, Mass. (1998) www.w3.org/TandS/QL/QL98/pp/maier.html

....Spouse, x2 ) new(x : newldO, Spouse, Xl ) new(xq : newd( Eva ) new(x. newd( Peter ) add(x, 5.2. Data retrieval features of PathLog In this subsection we will discuss some important features of PathLog. In queries Q1 Q3, we will base on the query examples originally proposed in [12] and used in [6] for comparison some query languages. The Manufacturer objects list the manufacturer s name, year, and models with their names, front rating, side rating and rank; the Vehicle objects list the vendor, make, model, color and price. We consider PLO data of the form: 1 Manufacturer ....

Maier D., Database desiderata for an XML query language, Proc. of the Query Languages Workshop, Cambridge, Mass. (1998).

....should allow similar forms of incomplete specifications in breadth, i.e. concerning siblings, and in depth, i.e. concerning children. Circularity. Queries and answers should be a queryable data items. This is more stringent than requiring an XML representation of queries. The requirements of [7] are fulfilled by or compatible with Xcerpt. 3 Xcerpt Basic Constructs Aspects of XML, such as attributes and namespaces, that are irrelevant to this paper, are not explicitly addresses in the following. The following pairwise disjoint sets of symbols are referred to: A set I of identifiers, a ....

D. Maier. Database Desiderata for an XML Query Language. In Proceedings of QL'98 - The Query Languages Workshop, 1998. http://www.w3.org/TandS/QL/QL98/.

....the basic DBMS concept of partitioning data and meta data. 3) The structure of documents to be stored is not necessarily constrained by any schema, i.e. it is possible to store such generic documents even if they do not come with any schema information. With respect to query languages, compare [6]. 4) Efficient operations on documents with respect to both Data Definition Language and Data Manipulation Language must be supported, especially operations that change the structure and the content of documents. 5) XML specific properties, in particular defined by the XML Information Set[28] ....

David Maier. Database Desiderata for an XML Query Language. http://www.w3.org/TandS/QL/QL98/pp/ maier.html, 1998.

....in breadth, i.e. concerning siblings, and in depth, i.e. concerning children. Circularity. Both, Xcerpt expressions and answers are query able using Xcerpt, i.e. they are XML data. Note that this is more stringent than an XML format for Xcerpt queries. Furthermore, the requirements of [8] are fulfilled by Xcerpt. 3 Basic Constructs of Xcerpt 3.1 Database Terms Database terms are XML documents in a simplified syntax. Following a common practice in XML query language and semistructured data research [1] the children of a document node may be either ordered (as in SGML and in ....

Maier, D.: Database Desiderata for an XML Query Language. In: Proceedings of QL'98 - The Query Languages Workshop. (1998) http://www.w3.org/TandS/QL/QL98/.

....query atoms may occur in bodies of construct query rules. 7 The syntax used in the present paper slightly departs from the Xcerpt original syntax. For example, a[X # b c, d , e] is expressed in Xcerpt original syntax as: element a [ X as element b element c; element d ; element e ] Following [8], Xcerpt programs are representable in XML, i.e. Xcerpt has an additional XML based syntax to be used e.g. for data interchange. Some issues deserve more investigations. The rich (and redundant) system of references of XML (with id idref attributes and links) needs a representation in Xcerpt. A ....

Maier, D.: Database Desiderata for an XML Query Language. In: Proceedings of QL'98 - The Query Languages Workshop. (1998) http://www.w3.org/TandS/QL/QL98/.

....Circularity. For the query language, queries and answers should be a queryable data items. Note that this is more stringent than requiring an XML representation of queries: e.g. the existence of JavaML does not make XML a data type directly accessible in Java. Note that the requirements of [9] are fulfilled by or compatible with the basic query language defined below. 3 Xcerpt Basic Constructs This section introduces the essential constructs of the query language Xcerpt. Aspects of XML, such as attributes and namespaces, that are irrelevant to this paper, are not explicitly addresses ....

Maier, D.: Database Desiderata for an XML Query Language. In: Proceedings of QL'98 - The Query Languages Workshop. (1998) http://www.w3.org/TandS/QL/QL98/.

....and other query languages, queries might have several answers, each answer binding the query variables di#erently. Symmetry. Queries should allow similar forms of incomplete specifications in breadth, i.e. concerning siblings, and in depth, i.e. concerning children. Note that the requirements of [4] are fulfilled by or compatible with the basic query language defined below. Below, the following pairwise disjoint sets of symbols are referred to: A set I of identifiers, a set L of labels (or tags or strings) a set l of label variables, a set t of term (or data item) variables. ....

Maier, D.: Database Desiderata for an XML Query Language. In: Proceedings of QL'98 - The Query Languages Workshop. (1998) http://www.w3.org/TandS/QL/QL98/.

....while unnest operates on a known structure (set valued attributes) 2. It has no notion of low level operations such as memory reference resolution (as in the materialize case) 1 The name of the project will not be disclosed for anonymity purposes. 2 The problem of querying over XML data has mainly been dealt with in the context of specific query language proposals. XML QL [DFF 98] was perhaps the first well known XML query language. Quilt [CRF00] is a recently proposed language that is rapidly growing in popularity. XSL [ABC 00] and XPath [CD99] have been proposed as ways to ....

.... input and output also help us avoid approaches such as the one in [MW99b] in which each edge traversal in the XML graph is represented by a di#erent operator (called Discover ) Once all traversals are accounted for, new operators (called Chain) are used to ensure the path expression structure remains intact. For instance, after retrieving vertices corresponding to author elements and vertices corresponding to book elements, they have to ensure that the author elements reside inside book elements (i.e. books are Chained with authors) An operator acting on the structure and not the value of ....

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David Maier. Database desiderata for an XML query language. http://www.w3.org/TandS/QL/QL98/pp/maier.html.

....[8] and X OQL [1] A survey of some of these languages can be found elsewhere [20] We do not claim that our query language, which is basically an extension of OQL, is more powerful or better than others. Instead, we use our own language because our goal is to capture the most important features [25] found in many of these languages in the simplest way possible and give them clean, compositional semantics. We believe that our semantics and transformations can also be applied to other languages, albeit with much more e ort. However, there are features lacking from our language, such as ....

D. Maier. Database Desiderata for an XML Query Language. In Query Languages 98 (QL'98), 1998. Available at http://www.w3.org/TandS/QL/QL98/pp/maier.html.

....these queries have an expressive power comparable to some well known relational operations (e.g. union and cartesian product) and therefore are essential for expressing many useful document restructuring operations. We also present in this paper the queries that were proposed by David Maier [9] for benchmarking the expressive power of query languages for XML, such as XML QL [5] Lorel [6] XQuery [4] XQL [11] and XSL [12] 2. PRELIMINARY OVERVIEW OF XMLGL XML GL relies on a graphical representation of XML documents and DTDs by means of labelled graphs, called XML graphs, where nodes, ....

....ELEMENT WITH PCDATA AND ID ATTRIBUTES text text value IDREF ATTRIBUTES E B A B text B Figure 3: Correspondence between the XML document components and the XML graph notation. Throughout the paper we will consider the document and the queries drawn from the running example proposed in [9] and use it as a comparative benchmark of the expressive 2 Note that the current DTD representation syntax may be refined for representing nested iterators, by allowing multiple cardinalities on arcs. power and intuitiveness of XML GL. Two kinds of document are defined: in the former, the ....

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D. Maier. Database desiderata for an xml query language. In Proc. QL'98 - The Query Languages Workshop, Cambridge, Mass., Dec. 1998. http://www.w3.org/TandS/QL/QL98.

....format, there remains the need for persistent storage in XML form to preserve the communications between different parties in the form understood and agreed to by the parties. David Maier proposed a list of language properties that are implied by the need to query collections of XML data [Mai98], and these have largely been adopted by the W3C XML Query Language Working Group [CFR01] In this paper we propose further capabilities that must be provided by database management systems that purport to support XML databases and their applications. The XML:DB initiative (http: www.xmldb.org) ....

....they connect are included in the view. The DDL must support the declaration of linkbases and their relationship to other data. 4. Desired DML characteristics The development of XML query languages has been based on extensive discussion about the desired characteristics of such languages [Mai98, CFM01]. We will not repeat all those characteristics here; instead we discuss those characteristics that are important for manipulating persistent XML data in a controlled way, in the context of a system having the definition capabilities described in Section 3. 4.1 Queries In an XML database we ....

D. Maier. Database desiderata for an XML query language. QL'98 -- The Query Language Workshop, W3C, Boston (December 1998).

....and more adequate for XML documents. We mention a third application of the inference of DTDs for XML documents in connection with databases: The importance of making use of DTDs whenever known to optimize the performance of database queries based on XML has been stressed by various authors, see [8, 11, 27, 33, 34]. Unfortunately, DTDs are not always transferred when XML documents are transmitted. Therefore, an automatic generation of DTDs can be also useful in this case, as well. A contribution to the GI community. Finally, one can consider this paper also as a contribution to the GI community: Many GI ....

D. Maier. Database desiderata for an XML query language. In Proc. QL'98 | The Query Languages Workshop, 1998.

....SSD XQL XML basics Mary . Name . Manager . Project Publications E Commerce John . Name . Manager Article . Chapter 2 3 . Fig. 1. An example query (left) and database (right) edge query languages for semistructured data [22, 12, 36] are not considered in this paper. Thus, only the select parts of queries are mentioned, possible construct parts are left implicit. Some of the articles retrieved by the query Q are common to several projects in the database D (Figure 1) Evaluated against the database D, the query Q ....

D. Maier. Database desiderata for an xml query language. In QL'98 - The Query Languages Workshop, 1998.

....primitive. In XML QL, XSL and XQL there is no update language. 3 Comparative examples In the following, wepresent a comparison of LOREL, XMLQL, XML GL and XQL on the basis of the query examples originally proposed byDavid Maier inaPosition Paper Database Desiderata for an XML Query Language [Mai98]# a preliminary version of the XML QL examples were originally presented byPeter Fankhauser in a message to the XML Query language mailing list (message of Dec 22, 1998) The underlying case study is that of a car dealer office, with documents from different auto dealers and brokers. The ....

D. Maier. Database desiderata for an XML Query Language. In Proc. of the Query Languages workshop, Cambridge, Mass., Dec. 1998, http://www.w3.org/TandS/QL/QL98/pp/maier.html.

....for such a language although the activity invested towards obtaining one is rather intense [33] and a standard should emerge soon. This is a complex issue that we will partially address here. We could have stated some desiderata for an XML query language. However, since we could not add much to [21], we prefer to simply endorse that proposal. 2 Finally, we believe that a declarative specification of XML views should encompass aspects that are typically not found in relational or object database views. This comes from Web applications that are by nature distributed. So, for instance, a view ....

....the data with DTD s DCD s. More precisely, in each tree, the children of internal vertices are ordered, the edges are labeled, and the leaves may contain references to vertices of the same or another tree. 2 We perhaps could add that ODMG [11] provides answers to many problems that are raised by [21] and in particular to some of the modeling and query language issues. Thus, we favor an approach in the spirit of Ozone [19] 2 states state id = s1 scode ID scode sname Idaho sname capital idref= c1 cities in idref= c1 cities in idref= c3 . state state ....

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D. Maier. Database desiderata for an xml query language. www.w3.org/TandS/QL/QL98/pp/maier.html.

....and storing [28] In this paper, we address, among others, the problem of integration of different XML schemata, i.e. the problem of integration of different DTDs. For this purpose, it is necessary to find out what kind of integration problems can be solved by XML and by corresponding DTDs. As [21] points out, a formal model for XML is needed to analyze the potential of XML. As a matter of fact, we can show by a grammar based formalism, namely the notion of xtrees and xschemes, that even very simple integration problems cannot be solved using pure DTDs. e.g. we can always find a DTD ....

D. Maier. Database desiderata for an XML query language. In QL98 - The Query Languages Workshop. W3C, 1998.

....XLink into the document tree model of XML. This too loose integration makes it dicult to rely on XSL for formatting XML documents with hypertext links a la XLink. 2.9 Query and Transformation Languages Query languages are needed when XML is used as a data model for databases. As discussed in [13, 68, 3] and in the rst section of this paper, this is a very promising direction of research. A number of database projects have investigated various aspects of using XML as a data model for databases, see in particular [1, 2, 9, 20, 30, 15, 21, 43, 11, 16, 32, 33, 31] The articles [28, 6] explain and ....

D. Maier. Database Desiderata for an XML Query Language. In The Query Languages Workshop, 1998.

.... on the Web for applications such as e commerce [1] astronomy [8] biomolecular biology [15] document management [9, 2] linguistics [39] thesauri and ontologies [25] They are formalized as trees or more generally as graphs [30, 27, 6] Query languages for semistructured data have been proposed [17, 29, 43] that, like SQL, can be seen as involving a number of variables [42, 4] but, in contrast to SQL, give rise to arrange the variables in trees or graphs re ecting the structure of the semistructured data to be retrieved. Leaving aside the construct parts of queries, answers can be formalized as ....

....occurs in a title element t (at any depth) of some articles y of projects x are retrieved by the following query Q: Project . Title Article Publications Manager cont XML . x y z t . The restructuring facilities of full edge query languages for semistructured data [17, 29, 43] are not considered in this paper. Thus, only the select parts of queries are mentioned, possible construct parts are left implicit. Assume that some of the articles retrieved by the query Q are common to several projects, as e.g. with the following database D: 1 Project ....

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D. Maier. Database Desiderata for an XML Query Language. In The Query Languages Workshop, 1998.

....for semistructured data proposed so far fail to meet these requirements. Fig.1 contains some classes of core requirements for any query language for XML. Every class contains a whole bunch of requirements. The most important ones will be discussed below. Some of the requirements are contained in [12, 28, 23]. The first requirement directly turns our fourth hypothesis into a requirement. We also touched the second requirement. It is partially a consequence of web awareness but has several implications. Identification and referenciability of queries to maximize possible reuse of queries are two core ....

....languages proposed so far (not even XQL [29] XQuery [15, 14] unnamed [5] XML Query [16] provides a mechanism to access these identifiers separately by e.g. iterating through them. A closure requirement is not necessarily a feature of a query language for XML (see also the discussion in [23]) Instead, the query language can be restricted to produce variable bindings. The part that then converts a query result into a representation (e.g. an XML document (see Requirement 5) can also be implemented using a style sheet language. This is essentially the approach taken by YAXQL. However, ....

D. Maier. Database desiderata for an XML query language. In [25], 1998.

....group s recommended language is compared. In this paper, we do not address several important but orthogonal issues, such as the environment in which an XML query language will be executed. Instead, we refer the reader to a comprehensive list of desirable language features and related issues [21]. We also refer the reader to a substantial body of research, including the motivation for and typical applications of semistructured data, 1, 4, 27] data models for semistructured data [24] 3 query language design [2, 6, 16] query processing and optimization [22] schema languages [3, 5, ....

D. Maier. Database Desiderata for an XML Query Language. In W3C Workshop on Query Languages for XML. http://www.w3.org/TandS/QL/QL98/pp/maier.html

.... We are interested in querying the structured contents of documents on the World Wide Web, as studied for example in [4, 7, 8, 13] In particular, we want to query the structure of XML documents, each of which may or may not adhere to a document type definition (DTD) As pointed out by Maier [10], it is important that when DTDs are available for documents, they should be exploited by the query language processor at compile time. This would allow for possible query formulation errors to be detected (e.g. the query result might be empty To appear in 2nd ACM Workshop on Web Information and ....

D. Maier. Database desiderata for an XML query language. In Proc. QL'98---The Query Languages Workshop, 1998.

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D. Maier. Database Desiderata for an XML Query Language, 1998. http://www.w3.org/TandS/QL/QL98/pp/maier.html.

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D. Maier. Database desiderata for an XML query language. Available from: http://www.w3.org/TandS/QL/QL98/pp/maier.html, 1998.

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D. Maier. Database desiderata for an XML query language. Available from: http://www.w3.org/TandS/QL/QL98/pp/maier.html, 1998.

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D. Maier. Database desiderata for an XML query language. Available from: http://www.w3.org/TandS/QL/QL98/pp/maier.html, 1998.

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D. Maier. Database desiderata for an XML query language. Available from: http://www.w3.org/TandS/QL/QL98/pp/maier.html, 1998.

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David Maier. Database Desiderata for an XML Query Language. In Position paper in W3C's Query Language Workshop, 1998.

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