Relational and XML Data Exchange (Synthesis Lectures on Data Management)

Data exchange is the problem of finding an instance of a target schema, given an instance of a source schema and a specification of the relationship between the source and the target. Such a target instance should correctly represent information from the source instance under the constraints imposed by the target schema, and it should allow one to evaluate queries on the target instance in a way that is semantically consistent with the source data. Data exchange is an old problem that re-emerged as an active research topic recently, due to the increased need for exchange of data in various formats, often in e-business applications. In this lecture, we give an overview of the basic concepts of data exchange in both relational and XML contexts. We give examples of data exchange problems, and we introduce the main tasks that need to addressed. We then discuss relational data exchange, concentrating on issues such as relational schema mappings, materializing target instances (including canonical solutions and cores), query answering, and query rewriting. After that, we discuss metadata management, i.e., handling schema mappings themselves. We pay particular attention to operations on schema mappings, such as composition and inverse. Finally, we describe both data exchange and metadata management in the context of XML. We use mappings based on transforming tree patterns, and we show that they lead to a host of new problems that did not arise in the relational case, but they need to be addressed for XML. These include consistency issues for mappings and schemas, as well as imposing tighter restrictions on mappings and queries to achieve tractable query answering in data exchange. Table of Contents: Overview / Relational Mappings and Data Exchange / Metadata Management / XML Mappings and Data Exchange

資料交換是在給定源架構的實例和源與目標之間的關係規範的情況下，尋找目標架構的實例的問題。這樣的目標實例應該在目標架構所施加的約束下正確地表示來自源實例的信息，並且應該允許在目標實例上評估查詢，並與源數據在語義上保持一致。資料交換是一個古老的問題，最近由於在各種格式中交換數據的需求增加，特別是在電子商務應用中，它重新成為一個活躍的研究主題。在本講座中，我們概述了關係和XML上資料交換的基本概念。我們舉例說明了資料交換問題，並介紹了需要解決的主要任務。然後，我們討論了關係資料交換，重點是關係架構映射、生成目標實例（包括規範解和核心解）、查詢回答和查詢重寫等問題。之後，我們討論了元數據管理，即處理架構映射本身。我們特別關注架構映射的操作，如合成和反向操作。最後，我們描述了XML上的資料交換和元數據管理。我們使用基於轉換樹模式的映射，並且我們展示了這些映射導致了一系列在關係情況下沒有出現的新問題，但是它們需要在XML中解決。這些問題包括映射和架構的一致性問題，以及對映射和查詢施加更嚴格的限制，以實現在資料交換中可處理的查詢回答。目錄：概述/關係映射和資料交換/元數據管理/XML映射和資料交換