An interesting piece by Michael Carey architect for Liquid Data at BEA re. Enterprise Information Integration from XML Journal.
Key quote.
Since the dawn of the database era more than three decades ago, enterprises have been amassing an ever-increasing volume of information - both current and historical - about their operations. For the past two of those three decades, the database world has struggled with the problem of somehow integrating information that natively resides in multiple database systems or other information sources (Landers and Rosenberg).
This is the root cause of many of the systems integration challenges facing may IT decsion makers. They want to exploit the new and emerging technologies, but the internal disparity of data and application logic presents many obstacles.
Michael had this to say in his introduction.
The IT world knows this problem today as the enterprise information integration (EII) problem: enterprise applications need to be able to easily access and combine information about a given business entity from a distributed and highly varied collection of information sources. Relevant sources include various relational database systems (RDBMSs); packaged applications from vendors such as Siebel, PeopleSoft, SAP, and others; "homegrown" proprietary systems; and an increasing number of data sources that are starting to speak XML, such as XML files and Web services.
Virtuoso (which coincedentally has been used to build and host this blog) has been developed to address the challenges presented above; by providing a Virtual Database Engine for disparate data and application logic (all the GEMs on this page have been generated on the fly using it's SQL-XML functionality).
Additional article excerpts:
With XQuery, the solution sketched above can be implemented by viewing the enterprise's different data sources all as virtual XML documents and functions. XQuery can stitch the distributed customer information together into a comprehensive, reusable base view.
A critical issue at this point is how sensistive the XML VIEW is to underlying data source changes. Enterprises are dynamic, so static XML VIEWs are going to be suboptimal in many situations. Applications are only as relevant as the underlying data fluidity served up by the data access (this issue is data format agnostic).
Virtuoso addresses this problem through its support of Persistent and Transient forms of XML VIEWs (which are derived from SQL, XML, Web Services, or any combination of these).
Final excerpt:
The relational data sources can be exposed using simple default XML Schemas, and the other sources - SAP and the credit-checking Web service - can be exposed to XQuery as callable XQuery functions with appropriate signatures.
Unfortunately XML Schemas aren't easy, so making this a requirement for producing XML VIEWs is somewhat problematic (or should I say challenging). Of course this approach has it merits, but it does put a significant knowledge acquisition burden on the end-user or developer. This is why Virtuoso also supports an approach based on SQL extensions for generating XML from SQL that facilitate the production of Well Formed and/or Valid XML documents on the fly from heterogeneous SQL Data Sources (this syntax is identical to the FOR XML RAW | AUTO | EXPLICIT modes of SQL Server). It can also use it's in-built XSL-T engine to further transform other non SQL XML data sources (and then generate an XML Schema for the final product if required and validate against this schema using it's in-build XML Schema validaton engine).
This article certainly sheds light on the kinds of problems that EII based technologies such as Virtual Databases are positioned to address.
There is a live XQuery demo of Virtuoso at: http://demo.openlinksw.com:8890/xqdemo