What Do You Know About Databases And XML?

Dare Obasanjo writes: "XML has become a pervasive part of significant segments of software development in a relatively short time. From file formats to network protocols to programming langauges, the influence of XML has been felt. I have written an overview of XML schemas, XML querying languages, XML-Enabled databases and native XML databases. Below is a shortened version of the article." Obasanjo's original OODBMS article has been updated to reflect more of the disadvantages between picking an OODBMS over an RDBMS.

Comments

Re:xml is an interchange format, not a storage for

[ergo98]

xml is an interchange format, not a storage format

Absolutely, positively agree. Not only is XML only an interchange format, but it only makes sense in some situations (for instance if we have an embedded piece of hardware that we have to communicate with, and we're communicating to it from a Windows box, and there is no shared common data encapsulation format, I'd greatly prefer XML (with XSD) vastly over Jimmy the Programmer making up his own data encapsulation format/documentation method/extraction system, but if I have two Windows machines running SQL Server and they're in a common security context and they'll never change, I'd use DTS or replication, not XML).

and MS SQL Server is seeing the same thing now that they've got the XML in theirs

The XML "in" SQL Server is surface fluff (I love SQL Server and I'm saying this as a good thing, not a bad thing). i.e. Some modules that'll convert an XML query to an underlying DB query, and the results back to XML, and some basic XML importing and exporting routines. This hasn't affected the underlying operations of SQL Server whatsoever.

Web-Apps need XML

[webmaven]

Separation of content, logic, and presentation is very difficult to do in current web-app developments environments.

The breakdown is not on the logic/content side of the equation, or the presentation/content side, but mainly in the presentation/logic arena.

Imagine an HTML designer who has mocked up a page for a web-app, and hands it off to the dev team for them to add in the neccessary laogic to dynamically include the user-name, current balance, contents of the shopping cart, etc. Depending on the exact paragdigm taht their tools use, they will either:

a) Chop up the page and include various fragments in the programs that are designed to emit said fragments at the opportune times to be assembled into a text stream eventually recived by a browser

or b) Various bits of logic get stuck into the page in oder to parameterize and/or conditionalize it, using either some sort of speacial tagging format or actual inlined blocks of code.

Whichever approach the dev team's tools use, the result is the same: the designer can no longer change the altered page.

Even in case b), which maintains some semblance of a coherent 'page', the designer cannot load the page-with-logic into their favorite visual editor and see anything resembling the actual page. They certainly can't edit it to change the look-and-feel without breaking the carefully constructed logic.

The end result is that the designer has no recourse other than to take their page design, change it, and hand it over to the dev-team again for them to re-include (in some cases re-code) all of their logic.

This is obviously a very wasteful approach.

Amazingly, there actually is a solution to this problem. It's called Template Attribute Language (TAL), and it solves the problem by adding programming directives to the page via XHTML attributes on the existing tags. The language is deliberately designed to only be suitable for presentation logic, relegating business logic code to some other objects, where the designer can't see them. This helps enforce the appropriate distinction between presentation logic and business logic that most current development environments ignore, thus encouraging their admixture.

Currently, TAL (and the related specifications TALES and METAL) are only implemented in one environment, but the language has been deliberately designed to be as platform agnostic as possible. Other implementations of the specification are possible, and even desireable.

Articles:

Zope Page Templates: Getting Started

Zope Page Templates: Advanced Usage

Using Zope with Amaya, Dreamweaver, and other WYSIWYG Tools