Distributed Application Specification Language
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The DASL Programming Language (Distributed Application Specification Language) is a high-level, strongly typed programming language originally developed at Sun Microsystems Laboratories between 1999 and 2003 as part of the Ace Project. The goals of the project were to enable rapid development of web-based applications based on Sun's J2EE architecture, and to eliminate the steep learning curve of platform-specific details.
DASL defines an application as a domain model with one or more graphical user interfaces, where a user interface is defined as a choreography of the domain model objects. The inclusion of the user interface as part of the application specification is a key and unique feature of DASL among languages that provide rapid domain modeling.
The DASL language is partially declarative and partially procedural. Description of object/data structures and persistence, and the description of the logical presentation, are declarative. Basic object constraints and behavior are declarative, while additional object behaviors are specified procedurally as methods. Queries can be defined either declaratively or by writing methods.
The language and development environment are a practical realization of the model-driven architecture (MDA) approach. The programmer uses DASL to produce the platform-independent model or PIM, and the language code generators automatically produce and deploy the platform-specific model or PSM. New PSMs may be introduced by writing new code generators.
Benefits of the DASL Language Approach
A key benefit of the DASL Language approach over 3rd generation (3GL) programming languages is that enterprise applications can be specified in a very concise and precise way that expresses the application logic clearly. A small enterprise application in DASL can typically be implemented in 8-10K lines of DASL code, which the DASL compiler then typically translates into 200K lines of Java, XML, SQL, and other implementation artifacts. The 200K line figure is typical of equivalent applications written using 3GLs.
The conciseness of DASL can be seen also in terms of the content of the two representations (DASL vs. the generated application code in Java/XML/SQL etc). Most of the DASL code describes business logic and business processes specific to the application, independent of the deployment middleware, frameworks, and presentation mechanisms. This core business logic typically represents only 2-5% of the generated application code. Thus, writing, understanding, and maintaining the application code is much easier at the DASL level than it is at the level of the generated code, in which the business logic is scattered within various implementation artifacts.
Another advantage of using DASL to write applications, rather than conventional 3rd generation languages and IDEs is that the DASL code is independent of middleware, GUI presentation frameworks, network topology, and other implementation technologies. As new middleware and frameworks are developed and evolve, existing DASL programs can be migrated to them without the need to re-implement them.
DASL combines a declarative syntax with a Java-like procedural syntax. The declarative part of the language enables defining applications at a higher level of abstraction than 3rd generation languages such as Java. In DASL, the programmer does not describe interprocess communication between client processes, web servers, application servers, and databases. Rather, the programmer describes the application as a set of related domain objects (including their behavior) and as a set of screens and actions.
In contrast to highly specialialized DSLs, DASL is Turing-complete. The behavior of domain objects can be expressed using a combination of declarative and procedural syntax. For example, constraints on objects and object attributes are expressed declaratively, but the constraint itself can be defined either as a declarative expression or procedurally.
A DASL application has two primary components: A business object specification (BOS) that describes the object domain model, consisting of persistent and transient objects representing the domain of the application, and an application usage specification (AUS) that describes the actions or use cases that may be performed on the domain model. The AUS is essentially the choreography of the domain objects into a series of screens and actions.
Full Language Description
The DASL language is described in a published Sun Labs technical report called The DASL Language: Programmer's Guide and Reference Manual.
Within Sun Microsystems
Around 1999, two Sun researchers, Bruce Daniels and Bob Goldberg, started a research project in Sun Labs called the 'Ace Project', with the goal of simplifying the creation of Java web-based enterprise applications. The Ace Language, now known as DASL, was developed by Goldberg, Daniels, and several other colleagues as part of this project.
The Ace project and language were featured in an article that appeared in June, 2002 on Sun's website, as well as in the January 2003 edition of Computing Research News entitled Sun Microsystems Laboratories: License to Innovate.
'Project Ace', the Ace DASL development environment, was demonstrated by Bruce Daniels as part of James Gosling's keynote address at the JavaONE conference in March, 2002.
On the business side of Sun Microsystems, the DASL Language was used to implement the public interface to the Sun Grid Compute Utility, known as the GridPortal.
Outside Of Sun Microsystems
Although Sun Microsystems has no plans to make a commercial implementation of the DASL Language available outside of Sun, it has in the past made the technology available to selected partners and conducted trials using the technology. DASL was featured in a white paper at TechRepublic, on the Association for Computing Machinery Portal, at the OOPSLA 2004 Conference, and on ZDNET.
Ongoing Language Development
Commercial use and enhancement of the DASL Language is ongoing at RD3 Software Corporation. The RD3 language enhancements and code generators for DASL have broadened the scope of the language from dynamic HTTP-style web applications to rich internet applications.
The DASL Language now supports the concept of forms and nested forms as part of the logical presentation. Information and actions can be logically grouped, and layout hints can be provided in the DASL program to help the presentation code generators produce nice-looking default user interfaces.
Presentation and navigation of recursive relationships, such as organization charts and family trees, has been added to the language.
The RD3 implementation of the DASL language has been made extensible. A third party programmer can write a code generator plugin in Java targeted to a specific DASL object class so that a new presentation pattern for that object is generated when an object of that class is presented in a DASL program. Defining a new presentation pattern no longer requires changes to the DASL language implementation framework.