Vianu, V. (2001), A web odyssey: from Codd to XML, in `Principles of Database Systems', ACM, pp. 1--15.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....Macro tree transducers (MTTs) EV85,CF82,FV98] are a well known model of syntax directed translation. They can be obtained by adding parameters (used as in a macro grammar [Fis68] to top down tree transducers. Recently, tree transducers have gained new interest, as a model of XML query languages [Via01]. In particular, the k pebble tree transducer [MSV00] has been proposed as a general framework which captures all known XML query languages. As it turns out, pebble tree transducers can be simulated by compositions of macro tree transducers [EM] In this paper we only consider total deterministic ....

V. Vianu. A Web Odyssey: From Codd to XML. In Proc. PODS'2001, pages 1-15. ACM Press, 2001.

.... life times, the two way pebble automata still recognize regular languages only [15] and this also holds when generalized to trees [8] Even more recently, a corresponding tree transducer model was proposed as a general model for XML based query languages: the so called pebble tree transducer [20, 28] (related models are considered in, e.g. 1, 21, 22] Here we study some theoretical properties of the pebble tree transducer of [20, 28] restricted to monadic trees, i.e. to strings: the two way nite state transducer with nested pebbles (pebble transducer, for short) For a string w, jwj ....

.... Even more recently, a corresponding tree transducer model was proposed as a general model for XML based query languages: the so called pebble tree transducer [20, 28] related models are considered in, e.g. 1, 21, 22] Here we study some theoretical properties of the pebble tree transducer of [20, 28] restricted to monadic trees, i.e. to strings: the two way nite state transducer with nested pebbles (pebble transducer, for short) For a string w, jwj denotes its length, and w(i) denotes its ith element. The empty string is denoted . For binary relations R and R , R R = f(a; c) j 9b : ....

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V. Vianu; A Web Odyssey: from Codd to XML, in: Proc. 20th ACM Symposium on Principles of Database Systems (PODS 2001), 1-15, 2001

.... life times, the two way pebble automata still recognize regular languages only [15] and this also holds when generalized to trees [8] Even more recently, a corresponding tree trans ducer model was proposed as a general model for XML based query languages: the so called pebble tree transducer [20,28] (related models are considered in, e.g. 1,21,22] Here we study some theoretical properties of the pebble tree transducer of [20,28] restricted to monadic trees, i.e. to strings: the two way finite state transducer with nested pebbles (pebble transducer, for short) For a string w, w[ ....

.... Even more recently, a corresponding tree trans ducer model was proposed as a general model for XML based query languages: the so called pebble tree transducer [20,28] related models are considered in, e.g. 1,21,22] Here we study some theoretical properties of the pebble tree transducer of [20,28] restricted to monadic trees, i.e. to strings: the two way finite state transducer with nested pebbles (pebble transducer, for short) For a string w, w[ denotes its length, and w(i) denotes its ith element. The empty string is denoted h. For binary relations R and R , R o R = a,c) 3b: a, ....

[Article contains additional citation context not shown here]

V. Vianu; A Web Odyssey: from Codd to XML, in: Proc. 20th ACM Symposium on Principles of Database Systems (PODS 2001), 1-15, 2001

....can be losslessly decomposed into one in BCNF, but some constraints may be lost along the way. The previous work was specific for the relational model. As new data formats such as XML are becoming critically important, classical database theory problems have to be revisited in the new context [26, 24]. However, there is as yet no consensus on how to address the problem of well designed data in the XML setting [10, 3] It is problematic to evaluate XML normal forms based on update anomalies; while some proposals for update languages exist [25] no XML update language has been standardized. ....

V. Vianu. A Web Odyssey: from Codd to XML. In PODS'01, pages 1--15.

....a data definition languageas wellas a data manipulation language. For commercial relationalDBMSs thes languages are well unders: od. As a lot of datais becoming available in XML [11] and much ofdatabas resbas h focus is s(32B from the traditional relational model tos 43H:BO:233: data and XML [1,6,5,9,10], itis important toundersO:2 new isB47 that aris in the context ofdes(I4BO: and querying XML. One se his(Q is theseB: tics of XML datas ecifications Traditionally, XML data was desH: ed byDTDs [11] But jusas in the relational context, where sereB SQL s create table mus bes333Q:BO ted with ....

V. Vianu. A Web odyssey: From Codd to XML. In PODS'01, pages 1--15.

....(2) high level mechanism for specification of XML data transformations. In this paper, we propose a method based on uniform tree transducers to address both of the above problems. The start point of our work are W3C s standards as well as transformation methods for XML data based on tree automata [4, 8 10]. The proposed method is a part of our project for processing semistructured data and XML [11 13] ....

Vianu, V.: A Web odyssey: from Codd to XML. In: Proceedings of the 20th ACM Symposium on Principles of Database Systems PODS 2001, ACM Press (2001) 1--15

.... considered in the 60s and 70s [28, 34] and are related to feature trees over an infinite set of features [22, 23] it was the advent of XML that initiated their systematic study [8] XML is a popular data format which is becoming the lingua franca for information exchange on the world wide web [37], and XML data is naturally modeled as unranked trees [25, 37] This connection made recent advances in unranked tree language theory foundational for XML related research in areas such as XML pattern languages [9, 24, 26, 27, 31] and XML schema languages [18, 29] Most crucial XML concepts are ....

.... to feature trees over an infinite set of features [22, 23] it was the advent of XML that initiated their systematic study [8] XML is a popular data format which is becoming the lingua franca for information exchange on the world wide web [37] and XML data is naturally modeled as unranked trees [25, 37]. This connection made recent advances in unranked tree language theory foundational for XML related research in areas such as XML pattern languages [9, 24, 26, 27, 31] and XML schema languages [18, 29] Most crucial XML concepts are closely related to unranked tree automata. For example, DTDs ....

V. Vianu. A Web Odyssey: From Codd to XML. In PODS'01, pages 1--15.

....can be losslessly decomposed into one in BCNF, but some constraints may be lost along the way. The previous work was specific for the relational model. As new data formats such as XML are becoming critically important, classical database theory problems have to be revisited in the new context [26, 24]. However, there is as yet no consensus on how to address the problem of well designed data in the XML setting [10, 3] It is problematic to evaluate XML normal forms based on update anomalies; while some proposals for update languages exist [25] no XML update language has been standardized. ....

V. Vianu. A Web Odyssey: from Codd to XML. In #######, pages 1-15.

....nition language as well as a data manipulation language. For commercial relational DBMSs, these languages are well understood. As a lot of data is becoming available in XML [11] and much of database research focus is shifting from the traditional relational model to semistructured data and XML [1, 6, 5, 9, 10], it is important to understand new issues that arise in the context of describing and querying XML. One such issue is the semantics of XML data speci cations. Traditionally, XML data was described by Document Type De nitions (DTDs [11] But just as in the relational context, where simple ....

V. Vianu. A Web odyssey: From Codd to XML. In PODS'01, pages 1-15.

....theory for XML researchers # Frank Neven University of Limburg frank.neven luc.ac. be 1 Introduction The advent of XML initiated a symbiosis between document research, databases and formal languages (see, e.g. the survey by Vianu [38]) This symbiosis resulted, for instance, in the development of unranked tree automata [3] In brief, unranked trees are finite labeled trees where nodes can have an arbitrary number of children. So, there is no fixed rank associated to each label. As the structure of XML documents can be ....

V. Vianu. A web odyssey: From Codd to XML. In (PODS 2001.

.... a rigid structure (such as the World Wide Web) and when data is integrated from heterogeneous sources (especially when new sources are frequently added) It is commonly agreed that data models and query languages, designed for well structured data, are inappropriate in such environments [1] [2]. XML (Extensible Markup Language) 3] is fast becoming the dominant standard for representation and interchange semistructured data on the Internet. Many heterogeneous information sources can structure their external views as repositories of XML data, no matter what their internal storage ....

V. Vianu, A Web Odyssey: from Codd to XML, Proc. of the 20th ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems, PODS'2001.

....20, 26] logic and constraint programming [29, 30] and linguistics [14, 19] Over the last few years, applications in information exchange have appeared that necessitate new tools for synthesizing tree processing code from a declarative specification. These applications all revolve around XML [1, 35]. In XML, data is naturally modeled as a tree, the access methods and manipulation tools take input in the form of tree transformations or transducers, and the interface specifications give preconditions using a combination of tree grammars and tree constraints. The XML context brings issues to ....

V. Vianu. A Web Odyssey: from Codd to XML. In PODS'01.

....of topics is heavily biased by the author s own research. Furthermore, we only discuss XML research issues which directly motivate the use of the automata presented in this paper. For a more general discussion on database theory and XML, we suggest the survey papers by Abiteboul [1] and Vianu [61] or the book by Abiteboul, Buneman, and Suciu [2] We do not give many proofs and the purpose of the few ones we discuss is merely to arouse interest and demonstrate underlying ideas. Finally, we mention that automata have been used in database research before: Vardi, for instance, used ....

V. Vianu. A web odyssey: From Codd to XML. In Proc. 20th Symposium on Principles of Database Systems (PODS 2001), pages 1--15, 2001.

....structure and contents of XML databases and is emerging as the standard XML schema language. With its roots in hypertext documents and SGML, the modeling capabilities of XML DTDs were very limited from a database perspective. Essentially, a DTD can be viewed as an extended context free grammar [Via01] or a (local) regular tree grammar [MLM01b] that simply specifies a set of element names (i.e. tags for typing the tree nodes) together with their possible nesting structure (via regular expressions) In particular, there are no built in or user defined data types, class or type hierarchies, ....

....including a comparison with traditional (E)ER models. XML DTDs are quite impoverished in terms of data modeling capabilities, e.g. there is no subtyping mechanism [LPVV99,PV00] Another area where XML schemas are relevant for XML querying is in type checking and type inference of queries: Via01] provides an overview on the problems in type checking XML queries. A typical type checking problem is to compute, as accurately as possible, the output type of a query, given the query expression and the type of the input document. XML Schema information can also be used for type checking XQuery ....

V. Vianu. A Web Odyssey: from Codd to XML. In ACM Symposium on Principles of Database Systems (PODS), 2001.

....structure and contents of XML databases and is emerging as the standard XML schema language. With its roots in hypertext documents and SGML, the modeling capabilities of XML DTDs were very limited from a database perspective. Essentially, a DTD can be viewed as an extended context free grammar [Via01] or a (local) regular tree grammar [MLM01b] that simply specifies a set of element names (i.e. tags for typing the tree nodes) together with their possible nesting structure (via regular expressions) In particular, there are no built in or user defined data types, class or type hierarchies, ....

....including a comparison with traditional (E)ER models. XML DTDs are quite impoverished in terms of data modeling capabilities, e.g. there is no subtyping mechanism [LPVV99, PV00] Another area where XML schemas are relevant for XML querying is in type checking and type inference of queries: Via01] provides an overview on the problems in type checking XML queries. A typical type checking problem is to compute, as accurately as possible, the output type of a query, given the query expression and the type of the input document. XML Schema information can also be used for type checking XQuery ....

V. Vianu. A Web Odyssey: from Codd to XML. In ACM Symposium on Principles of Database Systems (PODS), 2001.

....using application speci c techniques. However queries including wildcards may require exhaustive graph traversals. Goldman, Widom [44] and colleagues [77] proposed a system, called Lore, to store and query a semistructured database (which is modeled as a large rooted labeled directed graph; see [1, 88, 92] for a survey) Lore uses four kinds of indices to accelerate (regular) path expression searching. For each edge label l in the graph, a value index (Vindex) is used to index all the nodes that have incoming edges labeled with l and with atomic values that satisfy some condition. A text index ....

V. Vianu. A web odyssey: From Codd to XML. In Proceedings of the ACM SIGMOD-SIGACT-SIGART Symposium on Principles of Database Systems, 2001.

....data and document centric capabilities of XML queries. 5 Extending XOO7 to Document centric queries XML syntax is suited for semistructured data. Yet XML and semistructured data have subtle differences. Without dwelling on the details of XML, a simple abstraction of XML is a labeled ordered tree [28]. A tree representation of XML and semi structured data is interchangeable but a graph structure of both models has differences. Semistructured data model is based on unordered collections, while XML is ordered. Unique identifiers can be associated with elements in XML. References to such elements ....

V. Vianu. A Web Odyssey: from Codd to XML. Proceedings of 20th Symposium on Principles of Database Systems(PODS

....document centric capabilities of XML queries. 5 Extending XOO7 to document centric queries XML syntax is suited for semistructured data. Yet XML and semistructured data have subtle differences [ABS00] Without dwelling on the details of XML, a simple abstraction of XML is a labeled ordered tree [Via01] A tree representation of XML and semi structured data is interchangeable but a graph structure of both models has differences. Semistructured data model is based on unordered collections, while XML is ordered. Unique identifiers can be associated with elements in XML. References to such ....

V. Vianu. A Web Odyssey: from Codd to XML. Proceedings of 20th Symposium on Principles of Database Systems(PODS

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Vianu, V. (2001), A web odyssey: from Codd to XML, in `Principles of Database Systems', ACM, pp. 1--15.

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Victor Vianu. A Web odyssey: From Codd to XML. In Proceedings of ACM symposium on Principles of database systems (PODS), pages 1--15, Santa Barbara, California, May 2001.

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V. Vianu. A Web odyssey: from Codd to XML. In Proc. PODS, pages 1--15. ACM Press, 2001.

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V. Vianu. A Web odyssey: from Codd to XML. In Proc. PODS, pages 1--15. ACM Press, 2001.

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V. Vianu. A Web Odyssey: from Codd to XML. In PODS'01, pages 1-15.

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V. Vianu. A Web Odyssey: From Codd to XML. In Proc. of the 20th Symposium on Principles of Database Systems (PODS 01), 1--15, 2001.

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V. Vianu. A Web odyssey: From Codd to XML. In PODS'01, pages 1-15.

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