Description of the ATLAS platform.

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ATLAS is a software platform specially oriented to computer graphics applications that allows unsophisticated developers to include advanced features in their applications with no or very little extra information and effort.

The features of ATLAS include the splitting of the application in distinct processes that may be distributed over a network, a powerful configuration and scripting language, and several tools including a journaling facility and an input system to easily construct reasonable interfaces.

The most important aim that ATLAS wants to achieve is a high level of transparency to the developer. Almost all services that ATLAS offers to applications developed over it are techniques that normally require a lot of specialized programming. The emphasis in ATLAS 's design is to relief the programmer from this effort.

Many facilities offered by ATLAS , like distribution or the communications mechanism, must be totally managed by ATLAS in order to achieve the maximum transparency to the developer. The programmer need not know about these mechanisms and can concentrate on the objectives of his application.

In terms of functionality, ATLAS includes these objectives:

• Low level of parallelism: ATLAS applications feature several distinct processes running concurrently in the same or different machines in a network; processes encapsulate ATLAS components or user modules. The user implements routines that are accessible to other processes as remote procedures. Since the application is split in several processes, these need to communicate over the network and exchange data between possibly different architectures. The distribution of processes is managed by a centralized architecture (represented in the figure) where the master process distr is the center of each ATLAS application. This master process is then the most crucial one in this architecture and also in the communications mechanism because it is the communications center for each application.
  
  
  A sample execution of an ATLAS application
  
• Configuration and macro language: The ATL language is a modular language which is used by the developer to configure the application ---stating which processes belong to it---, to describe the interface of a process indicating the public routines that can be called by other modules, to define the interaction among processes and the dialogues of the application and also to obtain a rapid prototype. At run time the developer or the final user can modify and recompile modules written in this language. To the final user the ATL language is also useful because he can use it as a powerful macro language that allows him to better control the execution, or customize the environment. The virtual machine that interprets ATL code allows both synchronous and asynchronous calls to external routines. Some processes may therefore act as large batch processes that are executed concurrently with the application.
• Flexible journaling mechanism: This mechanism records the actions of the work session in order to be able to repeat this work session at any other time. This is needed in incremental design applications (in particular CAD-applications). The mechanism supports undo's and redo's and enforces the consistency of data recorded in the journal after editions or modifications of it.
• Fault-tolerance: Since the application is spread out among several hosts, it becomes more exposed to transient or permanent failures (of the communications or of any of the hosts involved). Fault-tolerance is transparently provided based on the journaling mechanism and on heartbeat messages sent by all processes so that their status can be assessed.
• Standardized input model: A great deal of effort in an application's development is spent in its user interface. ATLAS provides a uniform but flexible view of inputs that allows many different dialogue modes in a uniform way.
• Reusability: Each user module is completely isolated from others (in a separate process) except through a well defined interface described in ATLAS 's programming language. Thus new components can incorporate and use reliably old ones. This makes easy the integration of new subsystems.
• Support to processes of constraints solving and parametric design: ATLAS also includes some mechanisms like the global identification mechanism which making a simple association of a tag to every user input data solves some problems like checking of consistency in the journaling mechanism, the problem caused by volatile references in graphical input data and the use of symbolic data required by processes of constraints solving.