The XML Data Custodian
by Thomas Erl

Whether you use XML for content management, or as a universal data transfer format, there will come a time when you will need to begin authoring custom Schemas or DTDs. Data modelling with XML is much like modelling data for relational databases, and standards used to ensure consistency are just as important to future integration and interoperability requirements.

If you’re just beginning to incorporate XML into your enterprise, there is no better time to think of assigning someone the responsibility of owning and maintaining the format, structure, standards, business rules, and validation rules associated with your XML documents. The XML & Web Services Integration Framework (XWIF), part of the SOA methodology developed by SOA Systems, defines this role and calls it the "XML Data Custodian."

Ownership of XML Vocabularies

The XML Data Custodian will need to create new vocabularies on-demand for XML developers who need to work with corporate data in an XML format, and have to maintain and coordinate these vocabularies. This involves ensuring that XML tags produced for vocabularies correspond correctly to definitions of the same data already residing in databases, and also trying to prevent the creation of any redundant or duplicate meta tags for the same corporate data sets (even if the same corporate data exists in different repositories).

Ownership of DTDs or XML Schemas

Depending on which type of data validation method your organization standardizes on, one person should be in control of how this validation and document structure technology is designed. DTDs and XML Schemas contain DDL-like information that defines the structure of an XML document, the data types allowed, validation rules, and other business rule-like functionality.

Generally, every XML document will need to be linked to a DTD or XML Schema. So, in addition to providing an overall vocabulary, the XML Vocabulary Custodian will need to assist in defining the hierarchical structure of XML documents, as well as the contents of data integrity rules. Again, the additional challenge here is to keep this information synchronized with the data integrity and referential integrity rules already in existence in corporate repositories.

Additional complexities can be anticipated if XML is playing an application interoperability role, where data from multiple data sources is being merged. Here the DTD or XML Schema may need to represent data integrity rules for each repository.

Namespace Domain Administration

Finally, the responsibility of namespace partitioning will likely also be assigned to this role. Namespaces allow for the definition of a domain in which vocabularies are valid. Theoretically, an organization could be partitioned into several namespaces in which independent vocabularies could exist.

SOA Design Patterns by Thomas Erl
Foreword by Grady Booch
With contributions from David Chappell, Jason Hogg, Anish Karmarkar, Mark Little, David Orchard, Satadru Roy, Thomas Rischbeck, Arnaud Simon, Clemens Utschig, Dennis Wisnosky, and others.
Web Service Contract Design & Versioning for SOA by Thomas Erl, Anish Karmarkar, Priscilla Walmsley, Hugo Haas, Umit Yalcinalp, Canyang Kevin Liu, David Orchard, Andre Tost, James Pasley
SOA Principles of Service Design by Thomas Erl
Service-Oriented Architecture: A Field Guide to Integrating XML and Web Services by Thomas Erl
Service-Oriented Infrastructure:On-Premise and in the Cloud by Raj Balasubramanian, Benjamin Carlyle, Thomas Erl, Cesare Pautasso
Next Generation SOA:A Real-World Guide to Modern Service-Oriented Computing by Pethuru Cheliah, Thomas Erl, Clive Gee, Robert Laird, Berthold Maier, Hajo Normann, Leo Shuster, Bernd Trops, Clemens Utschig, Torsten Winterberg
SOA with .NET & Windows Azure: Realizing Service-Orientation with the Microsoft Platform by David Chou, John deVadoss, Thomas Erl, Nitin Gandhi, Hanu Kommalapati, Brian Loesgen, Christoph Schittko, Herbjorn Wilhelmsen, Mickey Williams
SOA Governance:
Governing Shared Services On-Premise & in the Cloud
by Stephen Bennett, Thomas Erl, Clive Gee, Anne Thomas Manes, Robert Schneider, Leo Shuster, Andre Tost, Chris Venable
SOA with Java by Raj Balasubramanian, David Chou, Thomas Erl, Thomas Plunkett, Satadru Roy, Philip Thomas, Andre Tost
Modern SOA Methodology: Methods for Applying Service-Orientation On-Premise & in the Cloud by Raj Balasubramanian, David Chou, Thomas Erl, Thomas Plunkett, Satadru Roy, Philip Thomas, Andre Tost
Cloud Computing: Concepts, Technology & Architecture by Thomas Erl, Zaigham Mahmood, Ricardo Puttini
Cloud Computing Design Patterns by Thomas Erl, Amin Naserpour

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