WDVL: Introduction to Directory Services Markup Language (DSML)

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Directory Services Markup Language (DSML) XMLizes LDAP

Directory Services Markup Language (DSML) is an XML schema for working with directories. If you want to access directories within XML programs, DSML allows you to stick with familiar XML syntax and tools. DSML is defined using a Document Content Description (DCD).

DSML is designed with Lightweight Directory Access Protocol (LDAP) directories in mind. LDAP is a TCP-based protocol for accessing online directory services. The main idea of DSML is to allow XML programmers to access LDAP-enabled directories without having to write to the LDAP interface or use proprietary directory-access APIs such as Microsoft's Active Directory Service Interfaces (ADSI). In addition, DSML could give you one consistent way to work with multiple dissimilar directories.

A typical DSML transaction works as follows: An XML application formats a query in DSML. The query is transported across an HTTP network and received by a DSML service, which translates the query into LDAP. Via LDAP, the data is retrieved from the directory and passed back to the DSML service, which formats the data in DSML and sends it back across the HTTP network to the application.

Here's a graphical view of the process:

Who Needs DSML?

DSML will be of practical use to you only if DSML interfaces provide the functionality you need. That will depend partly on whether DSML itself specifies the required functionality, and partly on whether there is robust DSML support for the directory or directories your application needs to access.

Let’s look at these two points one at a time.

The DSML Spec

The DSML spec is still fairly immature: DSML 1.0 was released in final form at the end of 1999. Work on DSML 2.0 started in earnest in the Fall of 2000. Participants want to produce an implementable 2.0 spec by Q1 2001.

The biggest limitation of DSML 1.0 is a lack of support for querying and updating. A query allows a client to request specific information from a directory, such as the first name, last name and phone number of all employees in the Accounting department. An update changes information in a directory. For instance, it might modify a phone number or address, delete a record, or add a record. DSML 1.0 provides a meta-language for expressing the data model and structure of a directory in XML. It doesn’t say anything about how to query or update directories. If you want to do queries or updates, you’ll have to go outside XML. Most likely, you’d use LDAP or a proprietary API like ADSI (Active Directory Services Interfaces).

DSML 2.0 will support querying and updating. Since most applications that use a directory need to query and/or update, 2.0 will be the first really useful version of the spec for most programmers. However, you could use 1.0, for instance, to implement a bulk import/export function for directory information.