UML Semantics FAQ. ECOOP 99 Workshop Proposal

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1 UML Semantics FAQ ECOOP 99 Workshop Proposal 1 Cover Page Title: UML Semantics FAQ Organizers: on behalf of puml (precise UML group), puml/ Stuart Kent (primary contact), Computing Laboratory, University of Kent, Canterbury, Kent, CT2 7NF, UK. s.j.h.kent@ukc.ac.uk Andy Evans, Department of Computer Science, University of York, Department of Computer Science, University of York, Heslington, York, YO10 5DD. andye@cs.york.ac.uk Bernhard Rumpe, Department of Computer Science, Munich University of Technology, Muenchen, Germany. Bernhard.Rumpe@in.tum.de AV Equipment: A PC projector, an OHP, a box of blank slides, whiteboards, pens and lots of paper. 2 Abstract UML is fast becoming the de facto standard notation for specifying and designing software. This may worry formalists, especially those working directly in software engineering, who, when they look at UML, find a language which has a semantics that is informal and full of gaps and inconsistencies. This workshop aims to bring together experts in industry and academia to agree a common context for work on UML semantics, which, it is hope, will provide valuable input to the ongoing UML revision process. The vehicle chosen is a UML Semantics FAQ (Frequently Asked Questions). The FAQ will provide answers to questions clarifying the role and need for semantics, the different approaches that can be taken, and highlight key problems. The organisers will bring to the workshop an unfinished FAQ a list of questions, some with only brief answers, some with none at all. We hope to leave the workshop with a list of (possibly different) questions, each with detailed answers where possible illustrated by examples taken from the official UML documentation. The FAQ will be published in the ECOOP workshop reader, together with a list of contributers and their affiliations. 3 Announcement & CfP We will not request papers as contributions, but instead for potential participants to send EITHER a question to attach to the FAQ, together with a brief explanation of why the question is important, OR an answer to one of the questions included in the draft FAQ. These contributions will be used to decide who to invite, in addition to participants who we would like to invite in any case because we already know that they are likely to make inter- UML Semantics FAQ ECOOP 99 Workshop Proposal 1

2 esting and significant contributions (e.g. Bran Selic of ObjecTime, Alan Wills of Trireme, Peter Gorm Larsen of IFAD, Jean Bezevin, etc.). Attached is a first draft of the WS announcement, including CfP and draft FAQ. 4 Organizers biographies The puml (precise UML) group was established a year or so ago as a loose consortium of academics and consultants to coordinate work on improving the precision of UML, both in its definition and its use. Semantics is clearly any area which needs attention in this context. puml tries to be open in its approach. For a current list of members and details for joining see The named representatives of puml, who will be responsible for leading and coordinating the workshop are: Dr Andy Evans: Lecturer in the Computer Science Department, University of York, UK. He is a co-founder of the puml group, and author of articles on developing formal analysis techniques for UML, and applying UML to the development of safety-critical real-time systems. On the UML'99 programme committee. Dr Stuart Kent: Senior Lecturer in Computing at University of Kent, UK, and consultant and trainer to industry on both sides of the Atlantic. Research active in the areas of visual modelling, OOD and CBD, with publications in major journals and conferences. On the programme committee for UML 98/9. Dr Bernhard Rumpe: Senior Researcher at the Munich Institute of Technology, Germany. He is a co-founder of the puml group, and author of many articles and formal methods and object technology, most recently on formalising aspects of UML. He is cochair of UML 99, and has organised many workshops at ECOOP and OOPSLA. 5 Workshop Reader The contribution of this workshop to the Reader will be the UML Semantics FAQ, itself. The organizers will take on the responsibility of writing a complete version of this FAQ for the reader, based on the work done at the workshop, and in consultation with the attendees. The FAQ will include a list of participants at the workshop. UML Semantics FAQ ECOOP 99 Workshop Proposal 2

3 ECOOP 99 Workshop UML Semantics FAQ - organised by puml Call For Participation (draft) Overview UML is fast becoming the de facto standard notation for specifying and designing software. This may worry formalists, especially those working directly in software engineering, who, when they look at UML, find a language which has a semantics that is informal and full of gaps and inconsistencies. This workshop aims to bring together experts in industry and academia to agree a common context for work on UML semantics, which, it is hope, will provide valuable input to the ongoing UML revision process. The vehicle chosen is a UML Semantics FAQ (Frequently Asked Questions). The FAQ will provide answers to questions clarifying the role and need for semantics, the different approaches that can be taken, and highlight key problems. The organisers will bring to the workshop an unfinished FAQ a list of questions, some with only brief answers, some with none at all. We hope to leave the workshop with a list of (possibly different) questions, each with detailed answers where possible illustrated by examples taken from the official UML documentation. The FAQ will be published in the ECOOP workshop reader, together with a list of contributers and their affiliations. The workshop is organised by the precise UML group (puml). It is the second of a series begun at OOPSLA 98. It is intended to hold another follow-up at OOPSLA 99, which may be preceded by an informal preparatory session at UML 99. puml The puml (precise UML) group was established a year or so ago as a loose consortium of academics and consultants to coordinate work on improving the precision of UML, both in its definition and its use. Semantics is clearly any area which needs attention in this context. puml tries to be open in its approach. For a current list of members and details for joining see Participation Attendance at the workshop will be by invitation only, as numbers will be limited. Participants should come prepared to work hard (see proposed format below). If you would like to be considered for participation you are asked to prepare: EITHER a question, together with an explanation of why you think this question is important and an answer if you have one; OR a reasonably detailed answer to one of the questions in the draft FAQ. A draft FAQ is appended to this call. UML Semantics FAQ Call For Participation (draft) 3

4 Proposed Format 00 Question brainstorm discuss approaches to answering questions on draft FAQ identify new questions reject or rephrase questions identify groups to work on different questions 60 Group work on questions (1st phase) formulate outline initial answers to questions assigned to group plough through UML documentation in search of illustrative examples 90 BREAK 120 Group work on questions (1st phase cont.) 180 Progress review reports on progress from groups reorganisation of groups, reallocation of questions as necessary update list of questions 210 LUNCH 270 Group work on questions (2nd phase) formulate more detailed and precise answers compile examples and sources 360 BREAK 390 Any Questions? one of the organisers will chair representative of each group takes a seat on the panel each group gets a chance to ask at least one of the FAQs (they choose which one they think is most important) each panel member gets to answer the question, beginning with the (a) panel member from the (a) group who prepared an answer person asking the question gets right of reply if time, opinions are taken from the floor 480 END UML Semantics FAQ Call For Participation (draft) 4

5 Draft FAQ 1 What is semantics? Semantics is the meaning of the notation in UML. It is not: Just a richer specification of behaviour (e.g. pre/post conditions). The UML meta-model. This (currently) is at best an abstract syntax. The official semantics of UML is currently expressed only in English. 2 What is semantics for? A semantics is required for a number of different and possibly confliciting purposes: To enable a single modeller to understand the import of the syntax they write, for example to be sure that code derived from a model truly reflects what that model is about, to be sure that she has captured a model that reflects the way users and domain experts perceive the world, etc. To enable modellers to share designs. This requires modellers to have a shared semantics of the notation; they must not mean different things by the same syntax. To support the construction of CASE tools that can make use of the semantics. For example, for tools to generate the code from models, for tools to be able to check consistency of models, for tools to be able to execute/simulate models. To ensure CASE tools obey an agreed, shared meaning, so that different tools will generate code that, for all intents and purposes, exhibits the same external behaviour, so that different tools come up with the SAME answer when checking the consistency of a model, etc. To ensure that the notation is based on a firm and agreed set of concepts, to remove redundancies from notations, or at least recognise that they exist, to remove ambiguity from the notation. In short to ensure that the notation set hangs together. 3 What is the most appropriate approach to take to defining a semantics? It depends what its for and who the audience is. Some examples: English and prototypical examples are probably appropriate for modellers to understand what is meant by the notation and for them to develop a shared meaning. A formal semantics is required to be sure that the notation is unambiguous, is integrated and redundancies recognised. A formal semantics which is amenable to automation is suitable for the development of CASE tools, though one must be careful that users of those tools can get the benefits of automation without needing to understand the finer points and language of the semantics. A programmer can use the compiler for a programming language without needing to understand the fine mathematical details of the semantics on which the compiler is based. UML Semantics FAQ Call For Participation (draft) 5

6 4 What semantics already exist for UML? In the official documentation, the semantics is embedded in the abstract syntax, OCL, dynamic semantic diagrams and in English. Furthermore, it is written down diagram by diagram; there has been little attempt to integrate the meanings of different diagrams. The (mis)match between state digarams and class diagrams is a classic example. There are many ambiguities and inconsistencies in the English, which leads different people to take different interpretations (and how many developers have looked at the semantics document anyway?). Aggregation is a classic example. The UML meta-model only describes the abstract syntax of the notations, and that also tends to be written down diagram be diagram, so overlaps at the syntax level are not even recognised, leading to redundancy in the meta-model. A number attempts at formal semantics for fragments of the language have been made. However, these tend to be of the mapping to an existing formal language form. The mapping tends to be driven by a desire for elegant mathematical characterisations of meaning which may not correspond to the intended meaning of the notations (the intended meaning can only be ascertained by asking users of the notation to make decisions). There is little attempt to convey the impact of these semantics to users in a form that users can understand. There are also spurious claims about how formal semantics can be used as the basis for sophisticated CASE tools. At best, most of the work helps to clarify and reduce ambiguity in the notation. 5 Pragmatically, is the semantics in the Official Documentation sufficient, or, indeed, sufficiently correct? Presumably no, or there wouldn t be much point in this FAQ. But why, exactly? 6 If I want to work on the semantics of UML, what should I do? Work within a framework consistent with this document. At the minimum this means: Identifying the target audience of the semantics. If mathematical, decide what is the impact of the mathematics from a user s perspective: syntactic changes (UML meta-model), semantic changes in a form the user can understand (e.g.?). If targeted on tools, be clear about what kinds of tools the semantics support. What can you now do automatically that you could not do before. If possible comment on why this important practically. If intended to remove ambiguity/redundancy, then clearly describe (e.g. with examples) where the ambiguities lie, and how your semantics removes the ambiguity/ redundancy. If possible, provide evidence that your proposal matches with users intuitions and intentions. Identify relationships of the proposed semantics to existing semantics, with formal theorems and proofs if possible (depending on the target audience). The same piece of semantics work may be written up for different target audiences, in which case different aspects will be stressed. This FAQ provides the basis for some standard templates and introductions to assist with production of papers, so that you can quickly place your work in the context of others. UML Semantics FAQ Call For Participation (draft) 6

7 Take a look at the puml website where you will soon find a bibliography of papers on UML semantics in various formats. Please let puml know of your work so that it can be registered and linked to from the puml website. 7 How can I be sure that my voice is heard and good ideas get into the UML standard? puml s goal is to coordinate semantics work on UML and feed that through appropriate channels to the OMG UML standardisation effort. We are currently working on opening up those channels. Our aim is not to compete with the OMG effort, but to complement it. So, you could get in touch with us. Whatever your chosen route, you should remember that the industry partners of the OMG are the ones who bear all the risks, so unless you represent one of these partners the best you can hope for is to offer advice. UML Semantics FAQ Call For Participation (draft) 7