The relationship between features and extensions

You may have noticed in the last lesson that the word feature  was introduced, and used almost interchangeably with the word extension. In practice they are very similar, but they aren't exactly the same thing. 

A feature, as used in TAO, gives the user the possibility of doing something on their TAO platform - it provides a functionality. The example in the last lesson was Data Access Control. This feature, as we said, provides the administrator of a TAO instance with the possibility of limiting the access of certain users to certain areas of that TAO instance.     

An extension, on the other hand, is the software implementation which provides the feature in question. It must be installed so that the feature is made available. In the example, an extension called taoDacSimple must be installed so that the Data Access Control  feature is available to users of that TAO instance (in this case, to the administrator).   

There isn't always a one-to-one relationship between features and the relevant extensions, however: sometimes you will need to install more than one extension in order to use a particular feature, and other times several features become available just by installing a single extension.

As it is the features which users are most interested in, the remainder of this course is organized in terms of the features which are available.  A description is given for each feature, along with a list of the TAO Products in which they are enabled, as well as the extensions which are required to use them.