Meta-information is information about information. Now you have the definition, what does this actually imply for computational systems? There are occasions where you naturally make use of meta-information: the schema of your database, directory services, information about a system's configuration, and so forth. Meta-information in each of these cases allows us to increase the flexibility of the system. For example, if the schema for a database is embedded within your application, then you have negated any possible reuse of the information in the database. Separating the schema from the application allows other applications to make use of the same information.

The more flexible our systems are, the greater the chance of survival they have in the ever-changing environment of the modern computing system. To be flexible, you need to support dynamic discovery and incorporate new services when they become available. The key to providing flexible systems lies in the amount of self-description within the system. Some programming languages support such self-description (a good example is reflection in Java). There is also support for dynamic discovery of objects and meta-information within CORBA. In this chapter we will explore why meta-information provides such flexibility and how existing facilities can provide meta-information.

A lot of work done has been done in the past couple of decades on reflection in object-oriented systems. Reflection is the ability of a system of objects to reason about itself.