For the past week or so, I've been thinking about the value proposition for virtual directory technology (Virtual-D). Since I was first introduced to it, Virtual-D was presented to me as a new way to sync data -- an alternative to metadirectories and traditional sync tools. So, I initially thought about its value in relation to that of metadirectory/sync (as in Virtual-D vs. Sync).
Today, a co-worker and I discussed the significant overlap in the two feature sets and the various scenarios that might call for one or the other. Our enlightened conclusion was that Virtual-D and sync tools are complimentary parts of a complete IdM solution.
Then, on the drive home, a light bulb went on. Virtual-D doesn't replace metadirectory, it replaces... [drum role] directory. Hence the name. In an end-to-end IdM solution where you might want multiple directory instances with application-specific attributes and/or security mechanisms, you can replace much of the cost and complexity of numerous directory instances with a Virtual-D solution.
If the goal is to LDAP-enable an application (e.g. SSO, white pages) with enterprise identity information from existing clean data stores, Virtual-D is much less complicated to implement than traditional sync solutions. It doesn't require another data store and it helps circumvent typical political data ownership issues. However, Virtual-D requires clean, current data.
So, if you don't have good identity data available, you might look to aggregate data from the numerous data sources around your enterprise and to create an enterprise directory (or database). This is probably best accomplished using traditional data sync tools. Then, Virtual-D can use that newly compiled identity data store to expose relevant subsets of your identity data to your various applications. And without the need for additional directory instances. And it does so regardless of the data layout or the technology used by the sync tools.
With Virtual-D in the toolbox, it's easy to see why your metadirectory and your enterprise directory don't actually need to be directories at all. They can be relational data solutions. It's easier to store, manage, and sync data in relational formats. And most companies already have relational database expertise (and usually even licenses). When it's time to expose the data to an application, Virtual-D presents it in LDAP format achieving application interoperability and minimizing risk by presenting only relevant attributes to each app.