The Coexistence of Relational and Native XML Databases

Transcription

1 The Coexistence of Relational and Native XML Databases Using HiT Software s winallora and TEXTML Server to bridge the native XML/RDBMS divide White Paper January 2003

2 Table of Content I - Introducing XML...3 II - Native XML Content Servers Vs. Relational Databases...4 TEXTML Server: A Native XML Content Server 4 Relational Database Management System (RDBMS) 4 Why Bridge Native XML Content Servers such as TEXTML Server with Relational Databases? 4 III - Bridging TEXTML Server and Relational Databases with winallora...5 winallora as a Bridge 5 TEXTML Server/winAllora Integration 7 winallora Mapper 8 winallora Engine 9 IV - Conclusion...10 Technical Paper by IXIASOFT & HiT Software 2

3 I - Introducing XML XML (extensible Markup Language) is a recommendation put forth by the World Wide Web Consortium (W3C) and is quickly becoming the dominant format for describing content on the Web. It is a meta-language designed to be both human and computer readable and it can be understood by virtually any software application. XML was conceived to enable separation of content from presentation to make content more easily accessible across the Web. Using XML technologies, a business user can create content once and publish it at any time, across many different mediums. The XML content can be presented in a user-friendly, professional format by means of using XSLT (XSL Transformation) style sheets. For example, an application can use various style sheets to present customized content according to the target audience: one style sheet for the web, another to publish the content to a PDA and another for print, as shown in Figure 1 below. Figure 1: Cross-media publishing with XML and XSLT Technical Paper by IXIASOFT & HiT Software 3

4 II - Native XML Content Servers Vs. Relational Databases TEXTML Server: A Native XML Content Server TEXTML Server is a native XML content server designed specifically to store, index and retrieve XML content. A native XML content server stores XML documents in their original format. It recognizes the document s structure without mapping to a specific database model. The XML document is the fundamental unit of storage. As a result, the physical structure of the document is preserved 100% and is never stored in tables. A native XML content server does not depend on schemas or DTDs and accommodates any wellformed XML document. Therefore, it is the ideal solution for managing semi-structured or unstructured content. Since there is no dependence on a predetermined structure, a native XML content server can store and retrieve heterogeneous document types and is well suited to applications that manage documents with different contents and structures. Relational Database Management System (RDBMS) A relational database is a collection of inter-related tables, each consisting of rows and columns. Data is stored inside these tables and all operations on data are performed on the tables themselves, producing additional tables as a result. When storing XML documents in a relational database, the various XML elements and attributes must be mapped to a pre-determined structure according to information contained in a DTD or XML schema. Therefore, RDBMS are best suited to managing structured data in tabular formats, especially if the data is not likely to change. Why Bridge Native XML Content Servers such as TEXTML Server with Relational Databases? Depending on the application and the type of content to be stored, both XML content servers and relational databases have their advantages. Relational databases are particularly good for storing and querying highly-structured information. As a query language, SQL is designed specifically to query structured data. In addition, RDBMS store data efficiently and with no redundancy because each unit of information is saved in only one place (normalization). RDBMS are also known for their reliability and scalability and can be accessed by a very large number of concurrent users. RDBMS were never designed to handle semi-structured content often stored as XML. Semistructured content is information considered to be more document-centric, that is, content of a more unpredictable, less structured nature: content that varies in length and type, with elements or attributes that are often empty or missing, and whose ordering is important. Examples of document-centric XML documents include books, technical documentation, legal briefs, patient health records and news content. Technical Paper by IXIASOFT & HiT Software 4

5 Semi-structured content is difficult to store in a relational database since it does not map easily to the row-and-column structure of a RDBMS. It becomes necessary to map data based on a predetermined, rigid database schema. You must shred data into many different tables (resulting in multiple joins and slow retrieval time) or a single table with many null columns. A native XML content server such as TEXTML Server easily accommodates semi-structured content. There are many situations when using a native XML content server is beneficial: XML documents with complex DTDs containing hundreds of elements, mixed content or recursive content models. It is much easier to maintain collections of XML documents using a native XML content server than to map those documents or even to store them as BLOBs in a RDBMS. Using a native XML content server in this context offers a more flexible storage solution as well as superior content search and retrieval performance. The IT environment in large organizations is very likely to have a mix of structured and semistructured data as well as data-centric and document-centric applications. Therefore, it appears that both native XML content servers and relational databases are essential tools; each responding to different needs within the IT environment. For example, a customer receives purchase orders (PO) in XML format and would like to save them natively as XML within TEXTML Server. At the same time, the PO information needs to be reflected in the back-office applications that are running relational databases. winallora can provide this bridge. III - Bridging TEXTML Server and Relational Databases with winallora As native XML content servers and relational databases are complementary technologies rather than competitive, it is likely that native XML content server market leaders like TEXTML Server will continue to coexist and exchange content with relational databases. In many cases, XML is generated by a RDBMS and stored in a native XML content server to facilitate content publishing. IXIASOFT selected HiT Software, the leading provider of XML- RDBMS mapping and transformation technology, and their solution winallora to facilitate the exchange of content between RDBMS and TEXTML Server. winallora strengths are highperformance, ease-of-use and seamless integration. winallora as a Bridge HiT Software's Allora is a family of XML-to-RDBMS integration middleware. It natively supports Sun's Java platform (jallora), and Microsoft's Windows COM architecture (winallora). Allora is a set of tools that can be integrated with server applications such as IXIASOFT s TEXTML Server. HiT Software's Allora aims to solve the problem of integrating any relational data source to any XML schema document. It can be used by Java application servers, Java Server Page applications, Visual Basic applications, C/C++/.Net applications, and Active Server Page applications. Allora features two major software components: the Allora Mapper and the Allora Engine. It also includes several corollary tools, including wizards for major IDE applications, adapters for different server applications, and Web service integration modules. Technical Paper by IXIASOFT & HiT Software 5

6 Figure 2 shows a typical system architecture of an end-to-end XML authoring and publishing application. In this architecture, winallora serves as a bridge between legacy content or XML content generated on the fly and stored in a RDBMS. In addition, winallora provides a conversion agent for XML content extracted from TEXTML Server and exported to a RDBMS. Figure 2: End-to-end XML authoring and publishing application Technical Paper by IXIASOFT & HiT Software 6

7 TEXTML Server/winAllora Integration winallora is integrated to TEXTML Server s Administration Console, as shown in Figure 3. Figure 3: winalloras's toolbar within TEXTML Server's Administration Console After you have installed winallora 3.1 or a later version, a new toolbar with three new icons appears in TEXTML Server s Administration Console. The left-most icon in the toolbar starts the winallora Mapper, which defines the TEXTML Server/RDBMS mapping; the two other icons provide wizards to import content from a RDBMS to a TEXTML Server document base, and export and insert TEXTML Server documents to a RDBMS. The Mapper interface is user-friendly and provides a natural framework for seamlessly integrating native XML content servers and relational systems across the enterprise. Technical Paper by IXIASOFT & HiT Software 7

8 winallora Mapper HiT Software's winallora Mapper is a GUI application that allows creation and editing of mapping definitions between a W3C Schema or DTD instance and table fields from a relational database. Data mapping is made by dragging-and-dropping items between the XML structure and the database structure. To reduce the syntactical complexity of XML Schemas and DTDs, the Mapper represents them in a simplified tree-view (see Figure 4). All relevant information from the database catalogue, such as data type, precision, and scale, is available through field definitions. Figure 4: winallora Mapper The Mapper also supports retrieval and definition of referential integrity constraints. These are used to perform meaningful joins among different relational tables. Other major functions include support for the creation of predicates (which are eventually translated to the SQL Where clauses), as well as support for SQL and XML expressions and dynamic parameters in predicate definitions. winallora also offers a complete set of APIs for programmatically automating the integration process using VBScript. Design-time mapping tools such as winallora use scripting to provide the freedom to operate on either SQL data (marshalling) or XML data (unmarshalling). Technical Paper by IXIASOFT & HiT Software 8

9 winallora Engine The winallora Engine imports and exports the data to and from the XML structure. The Engine is called when the Import from RDBMS and Export to RDBMS processes are started from TEXTML Server's Administration Console. The Engine is a set of COM interfaces that take the mapping definitions from the Mapper and process them to perform XML export or import. winallora supports any ODBC and OLEDB-compliant database including most relational databases such as Oracle, DB2, MS- SQL Server, Sybase, Pervasive, Pointbase or Timesten. Import from RDBMS When the Import process is started, winallora deposits the relational data in XML format according to a specific DTD or XML schema. Traditionally, this requires complex SQL, XML APIs and XSLT processing but it does not with winallora. The maintenance of those XML/RDBMS interfaces is made seamless for the same reason. Figure 5: Import from RDBMS Technical Paper by IXIASOFT & HiT Software 9

10 Export to RDBMS Users of Content Management applications would modify XML documents stored in TEXTML Server and would like the changes to be reflected in other applications or databases. The winallora Export to RDBMS feature enables TEXTML Server to export XML documents to just about any RDBMS. winallora can perform insert, update and delete operations on the relational database and still enforce its referential integrity. No programming is necessary as all the logic is included in the mapping definition of the winallora Mapper. Figure 6: Export to RDBMS IV - Conclusion Thanks to the TEXTML Server/RDBMS integration provided by winallora, IT departments with a large investment in relational database infrastructure can use TEXTML Server for specific XML content publishing projects without compromising existing infrastructure. The winallora integration with TEXTML Server provides a seamless bridge between structured relational data and contentrich semi-structured XML. Technical Paper by IXIASOFT & HiT Software 10