Client Server Architecture

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.

Open Network Computing (ONC) is the Sun architecture, with

third party alliances providing the missing pieces. Sun's

RPC is licensed by more than 300 companies, including DEC,

IBM, and Apple Computer. It is a lean, efficient RPC that

is particularly effective for installations not requiring

WAN support. Transport Independent Remote Procedure

Calls (TI-RPC) were co-developed by Sun and AT&T. TI-RPC

runs independent of the underlying network transport,

allowing applications to run unmodified over multiple

transport protocols including NetWare,PCNFS, AIX/6000,

Solaris, UNIX/SVR4, AIX/ESA. NetWise developed the

TI-RPC Application Toolkit source code generation

technology.

SAA is a collection of selected software interfaces,

conventions, and

protocols that are used as a framework for developing

consistent,

integrated applications across the major IBM computing

environments.

Four major components of this architecture are:

- Common User Access (CUA) defines conventions for GUI

look and feel.

- Common Programming Interface (CPI) provides languages,

tools, and APIs that give applications greater portability

and more consistent user interfaces across multiple

platforms.

- Common Communication Support (CCS) supports existing

communications standards, such as LU 6.2.

- Common Applications, written by IBM, will serve as

demonstrations of SAA concepts and make it easy for users

to migrate between systems.