We briefly discuss the potential of domain-specific languages and domain-specific modeling languages for ULSSIS engineering, some of the scaling challenges involved, and the possibilities for raising expressiveness beyond current levels

Heering, J. (Jan)

Mernik, M. (Marjan)

English

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Domain-Specific Languages as Key Tools for ULSSISEngineeringJan HeeringCWIKruislaan 413, 1098 SJ AmsterdamThe NetherlandsJan.Heering@cwi.nlMarjan MernikUniversity of MariborSmetanova 17, 2000 MariborSloveniamarjan.mernik@uni-mb.siABSTRACTWe briefly discuss the potential of domain-specific languagesand domain-specific modeling languages for ULSSIS engi-neering, some of the scaling challenges involved, and thepossibilities for raising expressiveness beyond current lev-els.Categories and Subject DescriptorsD.2.1 [Software Engineering]: Requirements/Specifica-tions—Languages; D.3.2 [Programming Languages]: Lan-guage Classifications—Specialized Application LanguagesGeneral TermsDesign, LanguagesKeywordsDomain-specific languages, ultra-large-scale systems1. THE WEB AS DSL BREEDING GROUNDDomain-specific languages (DSLs) are languages tailoredto a specific application domain. They offer substantialgains in expressiveness and ease of use compared with general-purpose languages in their domain of application, with anattendant reduction in software complexity. They variouslyact as enablers of the use and reuse of domain knowledge, astools for large-scale software development and software gen-eration, and as tools for end-user development and human-computer interaction [2]. Contrary to the definition givenin [3, Glossary], we emphasize that DSLs need not be pro-gramming languages in any conventional sense. In fact,one of their strengths is that they transcend the boundariesof programming proper. For instance, as domain-specificmodeling languages (DSMLs) they are gaining a footholdin model-driven engineering (MDE) [1]. Another exampleis the well-known syntactic metalanguage EBNF, which isPermission to make digital or hard copies of all or part of this work forpersonal or classroom use is granted without fee provided that copies arenot made or distributed for profit or commercial advantage and that copiesbear this notice and the full citation on the first page. To copy otherwise, torepublish, to post on servers or to redistribute to lists, requires prior specificpermission and/or a fee.ULSSIS’08, May 10–11, 2008, Leipzig, Germany.Copyright 2008 ACM 978-1-60558-026-5/08/05 ...$5.00.a purely declarative specification language. The DSL spec-trum is very broad, ranging from domain-specific program-ming to high-level modeling and specification to languagesthat are not meant to be executable at all.The WWW is a veritable breeding ground for DSLs. Thehuge activity in Web software development justifies largeinvestments in new DSLs and their standardization, withthe W3C playing a pivotal role. HTML, OWL, XML, WS-BPEL, WS-CDL, WSDL, SMIL, XForms, and UDDI are ex-amples of DSLs directly or indirectly spawned by theWWW.Many of them target aspects of service-oriented computing(SOC), a paradigm that has emerged in the context of theWeb.Using the WWW as an indicator, we expect that DS(M)Lswill play an important role in ULSSIS engineering. Thisview is shared by the SEI ULS report [3], which explicitlymentions DSLs in Section 6.4.1 (Expressive RepresentationLanguages). We think the potential of DSLs extends tosome other sections of the ULS report that do not mentionthem explicitly. Any ULSSIS will probably give rise to newparadigms, both general-purpose as well as domain-specificones.Taking a quick tour through the ULS report, we indicatesome (but by no means all) of the applications of DS(M)Ls inULSSIS engineering, some of the scaling issues involved, andthe possibilities for raising expressiveness beyond currentlevels.2. THOUSANDS OF PLATFORMSA platform is the combination of hardware and softwarethat provides a virtual machine that executes software andapplications. A ULSSIS will have thousands of platforms [3,Section 1.2]. In principle, platform independence can beachieved by moving to higher abstraction levels (specifica-tion, modeling). Platform Independent Models (PIMs) arealready current practice in MDE. Given a Platform Defini-tion Model (PDM), a PIM is refined to a Platform SpecificModel (PSM). For ULSSIS engineering this approach willhave to be be scaled up significantly. We envision that inULSSISs not only PIM to PSM transformations will be de-scribed using DSLs, but also PIM to PIM transformationsin support of model evolution.3. CONTINUOUS EVOLUTIONContinuous software evolution in a ULSSIS [3, Section 2.3]will not only be a problem for code but also for other soft-ware artifacts such as specifications, models, and deploy-ment scripts. All these artifacts can be represented usingappropriate DS(M)Ls. Hence, the crucial problem is theevolution of DSLs. What are the current techniques andwhat can be envisioned for the future? More research isneeded towards a more formal incremental approach. Forexample, in formal verification one has to repeat all veri-fications whenever new increments are added, not just toverify the increment. How to support evolution at the lan-guage level by providing more explicit support for softwareevolution? Another issue, but completely different, is howDSLs can be easily evolved. Can integration of change bedone using the technique known as staging? What aboutrun-time adaptation of a ULSSIS? Moreover, modificationof one representation should be reflected in other represen-tations. This problem can be nicely solved with DSLs sinceall other artifacts (documentation, code) should be automat-ically derived from the specification expressed in the DSL.4. EXPRESSIVE REPRESENTATION LAN-GUAGESAs stated in [3, Section 6.4.1] ULSSIS engineering requiresincreased language expressivity. The two basic approachesto scaling up expressivity are sacrificing generality and rais-ing the level of abstraction. The former is used by DSLsand the latter by modeling languages, with UML as theprime example. Both mechanisms are used simultaneouslyby DSMLs, but also by highly declarative DSLs. Like UML,DSMLs often have a graphical syntax, but apart from thisdifference, there is little to distinguish DSMLs from otherhighly declarative DSLs, whether graphical or textual.Both approaches to scaling up expressivity have their lim-itations. On the one hand, increased specialization leadsto an increase in the number of languages needed to covera given domain, with attendant interoperability problems.On the other hand, the expressivity gained from raising theabstraction level may have to be compensated for by pro-viding important “details” separately. At best, this leads toa beneficial separation of concerns, at worst to collections ofsoftware artifacts with hard-to-understand interdependen-cies. Despite these limitations, we do not think that special-ization and abstraction are at the end of their useful life asexpressivity scaling mechanisms.In its present stage, let alone for ULSSIS engineering,the semantics of modeling languages is insufficiently devel-oped [4]. It is usually given by model compilers or gen-erators implemented in general-purpose programming lan-guages. Such a semantics is inadequate from the viewpointof documentation and verification, and it cannot serve as abasis for automatic generation of language-specific tools suchas verifiers, test engines or debuggers. Also, model process-ing tools may interpret a model differently if DSML seman-tics is underdefined. In practice, multiple domains maybe involved, and the corresponding DSMLs and language-specific tools may have to be composed in some way.5. SCALED-UP VALIDATION, VERIFICA-TION, AND CERTIFICATIONDS(M)Ls may help to achieve at least part of the up-scaling of validation, verification, and certification requiredfor ULSSIS engineering [3, Section 6.4.2]. DSLs offer pos-sibilities for analysis, verification, optimization, paralleliza-tion, and transformation at a high level in terms of domain-specific constructs that would be much harder or unfeasibleif a general-purpose language is used. In the general-purposecase the software artifacts involved would be full of acciden-tal complexities hampering reliable recognition of domain-specific patterns.6. POLICY-BASED MODIFICATIONSWe see a role for DSLs in formal policy specification, witha view to check policy conformance partly or fully automat-ically as mentioned in [3, Section 6.5.2].7. HUMAN INTERACTIONAs stated in [3, Section 6.1] research on user centered spec-ifications and on modeling users and user communities isneeded. The main issue is how to represent user knowledgeand belief systems in such a way that they are comprehen-sible and analyzable. Again, we see the use of appropriateDSLs as a step toward achieving these goals. Moreover, dif-ferent GUIs can be generated from user specifications thatbetter suit specific users and their expectations as well asdifferent contexts.8. ADAPTABLE AND PREDICTABLE SYS-TEM QUALITYThe above-mentioned potential of DSLs for high-level spec-ification, analysis, verification, and transformation may alsogive them a role in specifying, analyzing, and controllingquality attributes of ULSSISs as mentioned in [3, Section 6.6].9. ORCHESTRATION AND CONTROLCoordination and control of actions in ULSSISs [3, Sec-tion 3.2] can be described using DSLs by specifying generalrules of behavior with an underlying adaptable algorithmthat govern changing constraints, missions, and function-ality of ULSSIS actors. Coordination of artifacts producedby multi-languages or among multi-languages (specification,modeling, programming, representation languages) can bedone with DSLs, too. But note that evolution of such multi-language systems is even harder.10. REFERENCES[1] J. Gray, J.-P. Tolvanen, S. Kelly, A. Gokhale,S. Neema, and J. Sprinkle. Domain-specific modeling.In P. A. Fishwick, editor, CRC Handbook of DynamicSystem Modeling, chapter 7. CRC Press, 2007.[2] M. Mernik, J. Heering, and A. M. Sloane. When andhow to develop domain-specific languages. ACMComputing Surveys, 37(4):316–344, 2005.[3] L. Northrop, P. Feiler, R. P. Gabriel, J. Goodenough,R. Linger, T. Longstaff, R. Kazman, M. Klein,D. Schmidt, K. Sullivan, and K. Wallnau.Ultra-large-scale systems: The software challenge of thefuture. Technical report, Software EngineeringInstitute, Carnegie Mellon University, 2006.http://www.sei.cmu.edu/uls/.[4] OMG. Workshop on Precise Behavior Semantics forDomain-Specific Modeling Languages, Jacksonville, FL,September 25 2007. http://www.omg.org/cgi-bin/doc?mic/2007-09-01...-09.

Domain-specific languages as key tools for ULSSIS engineering

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