Martin Gogolla

USE: A UML-based specification environment for validating UML and OCL

The Unified Modeling Language (UML) is accepted today as an important standard for developing software. UML tools however provide little support for validating and checking models in early development phases. There is also no substantial support for the Object Constraint Language (OCL). We present an approach for the validation of UML models and OCL constraints based on animation and certification. The USE tool (UML-based Specification Environment) supports analysts, designers and developers in executing UML models and checking OCL constraints and thus enables them to employ model-driven techniques for software production.

Validating UML and OCL models in USE by automatic snapshot generation

We study the testing and certification of UML and OCL models as supported by the validation tool USE. We extend the available USE features by introducing a language for defining properties of desired snapshots and by showing how such snapshots are generated. Within the approach, it is possible to treat test cases and validation cases. Test cases show that snapshots having desired properties can be constructed. Validation cases show that given properties are consequences of the original UML and OCL model.

On Formalizing the UML Object Constraint Language OCL

We present a formal semantics for the Object Constraint Language (OCL) which is part of the Unified Modeling Language (UML) – an emerging standard language and notation for object-oriented analysis and design. In context of information systems modeling, UML class diagrams can be utilized for describing the overall structure, whereas additional integrity constraints and queries are specified with OCL expressions. By using OCL, constraints and queries can be specified in a formal yet comprehensible way. However, the OCL itself is currently defined only in a semi-formal way. Thus the semantics of constraints is in general not precisely defined. Our approach gives precise meaning to OCL concepts and to some central aspects of UML class models. A formal semantics facilitates verification, validation and simulation of models and helps to improve the quality of models and software designs.

Validating UML models and OCL constraints

The UML has been widely accepted as a standard for modeling software systems and is supported by a great number of CASE tools. However, UML tools often provide only little support for validating models early during the design stage. Also, there is generally no substantial support for constraints written in the Object Constraint Language (OCL). We present an approach for the validation of UML models and OCL constraints that is based on animation. The USE tool (UML-based Specification Environment) supports developers in this process. It has an animator for simulating UML models and an OCL interpreter for constraint checking. Snapshots of a running system can be created, inspected, and checked for conformance with the model. As a special case study, we have applied the tool to parts of the UML 1.3 metamodel and its well-formedness rules. The tool enabled a thorough and systematic check of the OCL well-formedness rules in the UML standard.

Model transformations? transformation models!

Much of the current work on model transformations seems essentially operational and executable in nature. Executable descriptions are necessary from the point of view of implementation. But from a conceptual point of view, transformations can also be viewed as descriptive models by stating only the properties a transformation has to fulfill and by omitting execution details. This contribution discusses the view that model transformations can be abstracted as being transformation models. As a simple example for a transformation model, the well-known transformation from the Entity-Relationship model to the Relational model is shown. A transformation model in this contribution is nothing more than an ordinary, simple model, i.e., a UML/MOF class diagram together with OCL constraints. A transformation model may transport syntax and semantics of the described domain. The contribution thus covers two views on transformations: An operational model transformation view and a descriptive transformation model view.

Towards a semantic view of an extended entity-relationship model

Nearly all query languages discussed recently for the Entity-Relationship (ER) model do not possess a formal semantics. Languages are often defined by means of examples only. The reason for this phenomenon is the essential gap between features of query languages and theoretical foundations like algebras and calculi. Known languages offer arithmetic capabilities and allow for aggregates, but algebras and calculi defined for ER models do not. This paper introduces an extended ER model concentrating nearly all concepts of known so-called semantic data models in a few syntactical constructs. Moreover, we provide our extended ER model with a formal mathematical semantics. On this basis a well-founded calculus is developed taking into account data operations on arbitrary user-defined data types and aggregate functions. We pay special attention to arithmetic operations, as well as multivalued terms allowing nested queries, in a uniform and consistent manner. We prove our calculus only allows the formulation of safe terms and queries yielding a finite result, and to be (at least) as expressive as the relational calculi.

Verifying UML/OCL models using Boolean satisfiability

Nowadays, modeling languages like UML are essential in the design of complex software systems and also start to enter the domain of hardware and hardware/software codesign. Due to shortening time-to-market demands, “first time right” requirements have thereby to be satisfied. In this paper, we propose an approach that makes use of Boolean satisfiability for verifying UML/OCL models. We describe how the respective components of a verification problem, namely system states of a UML model, OCL constraints, and the actual verification task, can be encoded and afterwards automatically solved using an off-the-shelf SAT solver. Experiments show that our approach can solve verification tasks significantly faster than previous methods while still supporting a large variety of UML/OCL constructs.

Conceptual modelling of database applications using an extended ER model

Abstract In this paper, we motivate and present a data model for conceptual design of structural and behavioural aspects of databases. We follow an object centered design paradigm in the spirit of semantic data models. The specification of structural aspects is divided into modelling of object structures and modelling of data types used for describing object properties. The specification of object structures is based on an E xtended E ntity- R elationship (EER) model. The specification of behavioural aspects is divided into the modelling of admissible database state evolutions by means of temporal integrity constraints and the formulation of database (trans)actions. The central link for integrating these design components is a descriptive logic-based query language for the EER model. The logic part of this language is the basis for static constraints and descriptive action specifications by means of pre- and postconditions. A temporal extension of this logic is the specification language for temporal integrity constraints. We emphasize that the various aspects of a database application are specified using several appropriate, but yet compatible formalisms, which are integrated by a unifying common semantic.

OCL: Syntax, Semantics, and Tools

The Object Constraint Language OCL allows to formally specify constraints on a UML model. We present a formal syntax and semantics for OCL based on set theory including expressions, invariants and pre- and postconditions. A formal foundation for OCL makes the meaning of constraints precise and helps to eliminate ambiguities and inconsistencies. A precise language definition is also a prerequisite for implementing CASE tools providing enhanced support for UML models and OCL constraints. We give a survey of some OCL tools and discuss one of the tools in some more detail. The design and implementation of the USE tool supporting the validation of UML models and OCL constraints is based on the formal approach presented in this paper.

Expressing UML Class Diagrams Properties with OCL

The Unified Modeling Language UML is a complex language offering many modeling features. Especially the description of static structures with class diagrams is supported by a rich set of primitives. This paper shows how to transfrom UML class diagrams involving cardinality constraints, qualifiers, association classes, aggregations, compositions, and generalizations into equivalent UML class diagrams employing only binary associations and OCL constraints. Thus we provide a better understanding of UML features. By reducing more complex features in terms of basic ones, we suggest an easy way users can gradually extend the set of UML elements they commonly apply in the modeling process.