References. ▫ XQuery An XML Query Language. ▫ “XQuery from the Experts”. ▫ prohanlanlika.ga ▫ XQuery Tutorial. download and read online XQuery From The Experts A Guide To The W3C XML Query Language file. PDF Book only if you are registered here. And also You. , prohanlanlika.ga • Or: XQuery from the Experts, A Guide to the. W3C XML Query Language, by Don. Chamberlin et others, Howard Katz Editor.
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XQuery is based on XML in the same way that SQL is based on the relational prohanlanlika.ga A report on SQL/XML - much more readable than the specification itself. [XQueryExperts] XQuery from the Experts: A Guide to the W3C XML Query. XQuery is a declarative language in which a query is represented XQuery is based on OQL, SQL, XML-QL, XPath languages. 6 .. XQuery from the experts. this decision is the natural bias in the XQuery group towards data-oriented XML. of XSLT was for translating XML into display formats such as HTML or PDF.
BabelFish, where are you? XQuery is really three languages in one: The surface syntax is the most visible of the three and the one that users are most likely to come into contact with. For most purposes, this version of the language is XQuery. See examples of the surface syntax in the sidebar Syntax: A quick sampler. An alternative XML-based syntax replaces the surface language with one that's more tractable to machine processing.
See XQueryX, later in this article. A formal algebraic language describes the inner workings of an XQuery processor in quite a bit of detail. An underlying formalism The Data Model and Formal Semantics working drafts together provide a precise, theoretical underpinning for XQuery.
The two documents detail a query algebra, a set of precise definitions that define in formal terms the core entities that an XQuery query is expected to operate on, and formulations of what the various language operators can do with those operands.
This likely won't be of interest to you unless you're a query-engine implementer, have major pocket protection, or simply like working with complex, formal systems.
One mapping that's provided enables implementers to recast surface syntax features directly into the underlying algebra. You can implement query processors that actually speak the algebra directly although I would think this is more for proof-of-concept , as several vendors have demonstrated at XML trade shows. A link in Related topics points to an online demo version of one of these algebra-based engines. The algebra also provides rules that detail how to optimize and transmute both complex expressions into simpler equivalents.
As best I can tell I'm not a language theorist, and the Formal Semantics document is far from light reading , both of these are good things. Large database vendors in particular will appreciate a query-language architecture that's designed from the ground up to be both optimizable and efficient.
The algebra also provides a place to hang type information. The algebra has both static and dynamic typechecking capability. For example, an engine can use PSVI-derived type information to statically check the datatype of query expressions at compile time when the query's being analyzed for syntactic correctness.
Determining that a query is type-invalid early in the cycle short circuits the need for doing potentially expensive and fruitless searches against large datasets. Much of the work on the XQuery specification has involved work on the syntax and semantics of the part of the language involving types. The transition to XPath 2. XPath 2. The data model describes the core information in an XML document that's of interest to an XPath processor, and the final syntax and semantics of XPath's step operations is now almost completely worked out.
At times that's been challenging, both politically and technically. On the other hand, a poorly designed language can inhibit the acceptance of an otherwise promising technology.
The designers of XQuery took their responsibilities very seriously, not only in the interest of their individual companies, but also in order to make a contribution to the industry as a whole. It has been quite obvious that the designers of SQL had little understanding of data fundamentals in general, and the relational model in particular; and SQL was hardly developed in accordance with good language design principles.
If there were any doubts about that to this point, XML and XQuery make it perfectly clear that things are becoming worse, not better. It is not the seriousness with which XQuery specifications were undertaken that is in question here, but rather that of the knowledge and understanding of the specifiers, given that they are vendors. We will, therefore, expose just enough lapses to justify not bothering with the rest. In other words, if an application is viewed as a source of information in XML format, it is logical to pose queries against that XML format.
This is the basic reason why a query language for XML data is extremely important in a connected world. It is precisely because a majority in the industry is in that state that we warned early on that somebody somewhere would try to extend XML to data management, for which it was not originally intended, and where it does not belong. The industry has been doing this sort of thing ever since I can remember, with predictable consequences.
This principle had to be independent of any particular language or application and easily extensible to new and unanticipated kinds of information.
XML provides a neutral notation for labeling the parts of a body of information and representing the relationships among these parts. Since XML does not attach any semantic meaning to its labels, applications are free to interpret them as they see fit. Applications that agree on a common vocabulary can use XML for data interchange. Since XML does not mandate any particular storage technique, it can be used as a common interchange format among systems that store data in file systems, relational databases, object repositories, and many other storage formats.
We point out, in passing, that relational databases are not storage systems, to be lumped together with file systems. They are organized collections of data from which mechanized logical inferences are made. The purpose of the new query language was to provide a flexible facility to extract information from real and virtual XML documents. One of the earliest activities of the Query working group was to draw up a formal statement of requirements for an XML query language.
This document was quickly followed by a set of use cases that described diverse usage scenarios for the new language, including specific queries and expected results. In adding support for the XML typing system, extending the BBQ XML elements and attributes are shown in a directory- set of supported core functions and adding the capability of like tree and the users specify possible conditions and rela- querying the document order.
Equix, but restructuring capabilities the tool with constructs, primitives and capabilities specific are limited and aggregations are not supported. We are cur- is an integrated user interface that supports browsing and rently planning an attempt in this direction, in cooperation querying of object databases; PESTO allows users to navi- with a research group that develops a system for fast and ef- gate in a hypertext-like fashion, following the relationships ficient access to digital libraries with semi-structured data.
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