A directory schema is used to name objects, such as users, and attributes, such as addresses and telephone numbers.
Directories typically have their own unique schema.
The goal of DSML developers is to create a method for a directory to present its schema in a language common to all directories. DSML would be the mechanism for exchanging schema data, such as employee names or privileges, and for supporting user management and Web-based applications. But it is certainly not a panacea for interoperability. XML is a set of tags, much like HTML, for describing data. But they're all non-nirvana solutions.