One drawback of virtual directories is that they introduce a layer of middleware between the user and the authoritative system of record, which may translate into slower performance than users would experience with the authoritative system; this may be a problem only with apps that require a high service level, such as those for call centers. In addition, a virtual-directory application must be deployed with the same level of fault tolerance as the directory and database applications it will interact with.
Using The Data You Have
A virtual directory (and a metadirectory, for that matter) presumes two facts: The information users need exists in some enterprise application; and having users access that application directly is impractical, inefficient or inappropriate. In addition, companies may want to present data from multiple applications in a single view to give users all the information they need in one place. Without a virtual directory, companies would be faced with using a metadirectory to pull that information into an additional, more broadly accessible data store or with extending that information into an application to which users have been granted access--a customer-service program, for instance, through which users would see customer-contact information from a CRM application and shipping information from a logistics and supply-chain application all on a single screen.
With a metadirectory, IT admins must extend the metadirectory or application schema, then provide a mechanism that synchronizes data. The downsides of this approach include costly development, unreliable synchronization and information that is only as up-to-date as the last synchronization. In organizations subject to regulatory requirements, these changes also must be documented and justified for audit purposes.
Virtual directories, in contrast, let users access data structures already in place, regardless of format, while maintaining the authoritative app's security structure. Rather than replicate existing data as a metadirectory would, a virtual directory acts as a proxy to the authoritative app, passing security credentials, accessing records and transforming data so that it can be displayed to users in the proper context.
