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LDAP is a minefield. And it is not really like SQL. SQL is, well, like the name suggests, a standardized query language that you use to retrieve info from a database.
LDAP is a specialized database system optimized for storing contact type information and which provides very fast read access. Setting up and connecting to an LDAP directory is a chore, to say the least. It is no where near as straight forward as adding a datatable to your XOOPS DB and then querying it.
That's not to say it can't be done. And integration with LDAP is a very very cool thing, and very very useful.
However, if your organization does not already have an LDAP directory then I see absolutely no point in building this functionality into your module. None, you're just making extra work for yourself.
--Julian