What is the Point of Active Directory/LDAP Specification?

Question

My college threw an interesting curve ball today and I couldn't give him a good enough answer. The question was simple 'What is the point of active directory'. Now I don't have a lot of exposure to active directory, but I thought I could easily answer. My argument was; If you have a group of objects its easy to look up attributes for those objects using active directory. For example, if you have a group in AD and you want to verify the users of that group you simply look up the member attribute of that group. However he argued, rightly so, that you can do that with a table in a database, why do that in AD. I couldn't give him a good enough answer and now I'm curious. Given the above example, why use AD over a database?
To me AD is a way to manage a set of resources, whatever they are, by mapping them to objects that have however many attributes. But we could do that in a database, whats the point of AD? Why do you use AD?

Answer 1

I come from a primarily database centric background. Just like life experience, it casts a certain perspective on problems. Database people solve things with databases. Directory people solve things with directories. Everyone has their perspective. It's not really about who's right and who's wrong. It's about perspective because people are most likely to go with what's familiar when given a problem. It's easy to have this conversation in a educational environment but when you're on the job it's about turf, schedules and careers. My latest job (in which this debate comes up a lot) has been about directories which has been a very enlightening experience because I've been given a gift of perspective. I can put on the directory hat and look at it from another angle.
To get back to your professor's question. The answer is easy. LDAP (AD or other) is an application above a database. It has a data store behind it, in most cases we can just assume this is a database. So, in short, it's apples to oranges. But if we insist on comparing which makes the better juice, let's look at how we'd make a database like a directory. We could create a data model with an attributes table, an entries table and so on. We can deconstruct what LDAP data structures really are and implement each type as a table with FK/PK relationships and so on. It's sure to work because there are already so many products on the market doing this very thing. But think about the effort now. How are you going to add new users? A front-end? Stored procedures? Scripts? How are you going to keep someone from seeing things they shouldn't? You have to insert an object into all the right tables to ensure that your data is consistent and valid. In a pure database, you're trying to create ACLs on database rows. Now you're writing a full featured application with a lot of complexity. Given enough directory features, the database isn't going to be able to do everything without an external application.
What is the point of LDAP? It's got hierarchy, ACLs, group of unique names functionality and things that are a layer of abstraction above the data store. I love databases but if you start designing out a directory server from scratch you'll realize it's far beyond comparing a user.ldif to a row in a user table. They are similar in appearance but different types of software.
Edited by: milkfilk on Dec 16, 2008 11:48 AM
Edited by: milkfilk on Dec 16, 2008 11:54 AM