View De nition and DTD Inference for XML
View De nition and DTD Inference for XML
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XML 的视图定义和 DTD 推断
DOI：
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发表时间：
1999
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通讯作者：
V. Vianu
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作者：
Bertram Ludäscher;Y. Papakonstantinou;P. Velikhov;V. Vianu
我们提供了XML数据[XML98B]的查询语言和调解器体系结构。查询语言，称为XMAS（XMLMatching和构造语言）使用垂直和水平导航。水平导航提供了一种强大的新颖机制，用于使用XML的半结构模型中的顺序。这与垂直导航的众所周知的常规路径表达式很好[SUC，ABI97，BUN97，AQM97，FFLS98，AM98，CDSS98，XML98A，KS95]。圣诞节还提供了用于构建XML文档作为查询的答案的多功能机制，包括强大的组和订单结构。我们提出了一个基于XMA的基于XML的信息中介系统的原型。 DTD可以在创建集成视图和查询XML数据时具有多种用途。我们的原型使用视图DTD驱动的QBE风格查询接口。调解员将使用DTD来优化其发送给来源的查询。最后，DTD可以指导样式表的生产，例如XSL脚本[XSL98]，将XML文档显示为浏览器友好的HTML文档。 DTD也可能有助于设计存储结构。因此，很明显，集成观点的DTD将特别有用。但是，“通过深入探究源DTD的详细信息是错误的，并且可能成为集成软件开发的瓶颈，从而损害了半自动数据集成的大部分优势。调解器是DTD推理模块。 Xmas查询的视图中的DTD推断。通过这些扩展，我们表明可以通过选择查询来推断出视图的紧密DTD，从而从输入中提取元素列表精确地表征了满足DTD的来源的文档，我们还显示了有趣的特殊情况，我们可以在不需要扩展的情况下得出一个紧密的DTD。最后，我们考虑了相关的问题，例如检查与NED DTD的视图符合性的一致性。
We present a query language and mediator architecture for XML data [XML98b]. The query language, calledXmas (XMLMatching And Structuring Language) uses vertical and horizontal navigation. The horizontal navigation provides a powerful novel mechanism for using the order in the semistructured model underlying XML. This couples nicely with the well-known regular path expressions for vertical navigation [Suc, Abi97, Bun97, AQM97, FFLS98, AM98, CDSS98, XML98a, KS95]. Xmas also provides versatile mechanisms for constructing XML documents as answers to queries, including powerful group-by and order-by constructs. We brie y describe a prototype for an XML-based information mediation system, built around Xmas. DTDs can have multiple uses in creating integrated views and querying XML data. Our prototype uses a QBE-style query interfaces driven by the view DTD. The mediator will use DTDs to optimize the queries it sends to the sources. Finally DTDs may guide the production of style sheets, such as XSL scripts [XSL98], that display XML documents as browser-friendly HTML documents. DTDs may also help in the design of the storage structures. Thus, it is clear that DTDs of integrated views will be particularly useful. However, creating a view DTD \manually" by delving into the details of the source DTDs is error-prone and may become the bottleneck of the integration software development, compromising much of the advantage of semi-automatic data integration. A central component of our mediator is a DTD inference module. After outlining the architecture of the mediator and illustrating Xmas, we present work in progress and results (submitted for publication [PV98]) on DTD inference in views de ned by Xmas queries. We point out several strong limitations of DTDs and the need for extending them with (i) a subtyping mechanism and (ii) a more powerful speci cation mechanism than regular languages, such as contextfree languages. With these extensions, we show that one can always infer tight DTDs for views de ned by selection queries, which extract a list of elements from the input. The tight DTD precisely characterizes the documents in the view on sources satisfying given DTDs. We also show interesting special cases where we can derive a tight DTD without requiring the extension with subtyping. Finally we consider related problems such as checking conformance of a view de nition to a prede ned DTD.