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.