Appendix A - LDAP - Some Notes on Structuring Directories

This note discusses structuring LDAP directories in very general terms. Directory structuring is a horribly contentious subject and books have been written about it. The following notes may help - or there again they may not.

We look at a simple address book example to isolate some general principles - but they could apply equally well to equipment records, catalogues or whatever.

Flat is Good

Directories in general are typically very flat in structure 2 or 3 levels of hierarchy are common - more than that are pretty unusual. While on first glance this seems a little counter intuitive to classic database guys remember LDAP is optimized to power ALONG a level rather than UP and DOWN a hierarchy. That is the whole reason for the powerful indexing methods.

A simple example may suffice to illustrate: When looking at a company and structuring a directory it's pretty obvious the first split is by department. BUT IS IT? The following diagrams show two ways to structure a directory.

DIT 1 makes department an ou entry, DIT 2 makes department an ou attribute of entries under an ou of people. Sounds like a trivial difference.

Now lets look at finding some typical data:

1. Find all the people in sales:

   1. DIT 1 - Search DN ou=sales,dc=mycompany,dc=com, scope - one level, filter cn=*

   2. DIT 2 - Search DN ou=people,dc=mycompany,dc=com, scope - one level, filter ou=sales

   About the same.

2. Find all the people in the company:

   1. DIT 1 - Search DN dc=mycompany,dc=com, scope - sub (all levels), filter cn=*

   2. DIT 2 - Search DN ou=people,dc=mycompany,dc=com, scope - one level, filter cn=*

   Structure 2 wins - in speed and simplicity.

Lazy is Good

We'll stick with our structures and perform a simple task: Bill just moved from sales to marketing (a separate corporate department).

1. DIT 1 - Export Bill's record to an LDIf file, delete it from sales, edit the LDIF file, ldapadd the record to marketing. And hope he does not do this too often.

2. DIT 2 - modify Bill's ou attribute from sales to marketing.

Wonder who won that round.

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