VITAL provides a way of building information systems constructed from 
generalized modules that can be reused and shared.It specifies how to 
construct and provide interfaces for these modules. A cornerstone of 
Apple's client/server architecture is Data Access Language (DAL).  DAL 
consists of software components for the client and the server (Macintosh 
System 7 includes the client component, DOS and Windows clients are 
sold separately).  DAL sits between the client and server components.  
This approach allows varied clients to communicate with many different 
servers.  With DAL, a change in the DBMS does not affect the front-end; 
it simply requires the appropriate DAL link.