Azzam Maraee

Efficient reasoning about finite satisfiability of UML class diagrams with constrained generalization sets

UML class diagrams play a central role in the design and specification of software, databases and ontologies. The model driven architecture approach emphasizes the central role that models play, towards achieving reliable software. It is important that models are correct and that problems are detected as early as possible in the software design process. However, current case tools do not support reasoning tasks about class diagrams and enable the construction of erroneous models. There is an urgent need for methods for detecting analysis and design problems. In this paper, we present a linear programming based method for reasoning about finite satisfiability of UML class diagrams with constrained generalization sets. The method is simple and efficient and can be easily added to a case tool. It improves over existing methods that require exponential resources and extends them to new elements of class diagrams.

Finite satisfiability of UML class diagrams with constrained class hierarchy

Models lie at the heart of the emerging model-driven engineering approach. In order to guarantee precise, consistent, and correct models, there is a need for efficient powerful methods for verifying model correctness. Class diagram is the central language within UML. Its correctness problems involve issues of contradiction, namely the consistency problem, and issues of finite instantiation, namely the finite satisfiability problem. This article analyzes the problem of finite satisfiability of class diagrams with class hierarchy constraints and generalization-set constraints. The article introduces the FiniteSat algorithm for efficient detection of finite satisfiability in such class diagrams, and analyzes its limitations in terms of complex hierarchy structures. FiniteSat is strengthened in two directions. First, an algorithm for identification of the cause for a finite satisfiability problem is introduced. Second, a method for propagation of generalization-set constraints in a class diagram is introduced. The propagation method serves as a preprocessing step that improves FiniteSat performance, and helps developers in clarifying intended constraints. These algorithms are implemented in the FiniteSatUSE tool [BGU Modeling Group 2011b], as part of our ongoing effort for constructing a model-level integrated development environment [BGU Modeling Group 2010a].

Removing Redundancies and Deducing Equivalences in UML Class Diagrams

The emerging Model-driven Engineering approach puts models at the heart of the software development process. The Class Diagram language is central within the UML. Automated support for class diagrams involves identification and repair of correctness and quality problems.

Simplification and Correctness of UML Class Diagrams --- Focusing on Multiplicity and Aggregation/Composition Constraints

Model-driven Engineering requires efficient powerful methods for verifying model correctness and quality. Class Diagram is the central language within UML. Its main problems involve correctness problems, which include the consistency and the finite satisfiability problems, and quality problems, which include the redundancy and incomplete design problems. Two central constraints in class diagrams are the multiplicity and the aggregation/composition constraints. They are essential in modeling configuration management, features, biology, computer-aided design and database systems. The contribution of this paper involves efficient algorithms for tightening multiplicity constraints that cannot be realized, and for identification of correctness problems that are caused by aggregation/composition constraints. The algorithms are analyzed, and their soundness and completeness properties are proved. We show that these constraints are inter-related, and that the combination of these algorithms strengthens their results.

Inter-association constraints in UML2: comparative analysis, usage recommendations, and modeling guidelines

UML specification is verbal and imprecise, the exact meaning of many class diagram constructs and their interaction is still obscure. There are major problems with the inter-association constraints subsets, union, redefinition, association specialization, association-class specialization. Although their standard semantics is ambiguous and their interaction unclear, the UML meta-model intensively uses these constraints. The paper investigates the semantic implications of the above inter-association constraints, their interaction with other constraints, and implied correctness problems. Based on this study, we present a comparative analysis of these constraints, that includes characterization, and refers to complexity factors, and usefulness aspect. This analysis yields recommendations concerning the semantics and usefulness of the constraints. In addition, we present modeling guidelines for users. To the best of our knowledge, this is the first all inclusive analysis of the inter-association constraints in UML2.

Efficient recognition of finite satisfiability in UML class diagrams: Strengthening by propagation of disjoint constraints

Models lie at the heart of the emerging Model-driven Engineering approach. In order to guarantee precise, consistent and correct models, there is an urgent need for efficient reasoning methods for verifying model correctness. This paper extends and strengthens our previous work on efficient recognition of finite satisfiability problems in UML class diagrams with constrained generalization sets. First, algorithm FiniteSat is simplified into a single stage process, yielding a more compact linear inequality system. The main contribution of the paper is a method for propagation of disjoint constraints within complex class hierarchy structures, which meaningfully extends the scope of the FiniteSat algorithm. The method relies on a thorough analysis of the interaction between disjoint constraints and the structure of class hierarchy. It is recommended as a pre-processing stage, and being an anytime algorithm, even partial application is useful.

Consistency of UML class diagrams with hierarchy constraints

UML class diagrams are probably the most important, well-established, UML model. They play an essential role in the analysis and design of complex systems. UML class diagrams allow the specification of constraints such as cardinality constraints, class hierarchy constraints and inter-association constraints. Constraints extend the expressivity of class diagrams, but enable the specification of unsatisfiable class diagrams, i.e., class diagrams that have no finite non-empty instance world. Nowadays, UML case tools still do not check satisfiability of class diagrams, and implementation languages still do not enforce design level constraints. But the expectation is that in the future, and in particular with the prevalence of the Model Driven Engineering approach,all information in a design model will be effective in its successive models. In this paper, we present an algorithm for testing the satisfiability of UML class diagrams that include class hierarchies with “disjoint/overlapping” and “complete/incomplete” constraints. The algorithm is based on a reduction to a previous algorithm of Lenzerini and Nobili that was applied only to ER-diagrams without class hierarchies. Our algorithm is simple and feasible since it adds in the worst case only a linear amount of entities to the original diagram. It improves over previous elaboration of the Lenzerini and Nobili method that require the addition of an exponential number of new entities to the original diagram. An implementation of our method within a UML case tool is currently under development.

A pattern-based approach for improving model quality

UML class diagrams play a central role in modeling activities, and it is essential that class diagrams keep their high quality all along a product life cycle. Correctness problems in class diagrams are mainly caused by complex interactions among class-diagram constraints. Detection, identification, and repair of such problems require background training. In order to improve modelers’ capabilities in these directions, we have constructed a catalog of anti-patterns of correctness and quality problems in class diagrams, where an anti-pattern analyzes a typical constraint interaction that causes a correctness or a quality problem and suggests possible repairs. This paper argues that exposure to correctness anti-patterns improves modeling capabilities. The paper introduces the catalog and its pattern language, and describes experiments that test the impact of awareness to modeling problems in class diagrams (via concrete examples and anti-patterns) on the analysis capabilities of modelers. The experiments show that increased awareness implies increased identification. The improvement is remarkably noticed when the awareness is stimulated by anti-patterns, rather than by concrete examples.

On the interaction of inter-relationship constraints

MDE and software evolution call for model-level design support, that includes reasoning capabilities such as query answering, verification and validation, static analysis and model transformation. Automation of all activities requires well-defined semantics for models. This is particularly important for the class diagram model, which is central in UML. However, since UML specification is verbal and imprecise, the exact meaning of many class diagram constructs and their interaction is still obscure. There are major problems with the inter-association constraints subsets, union, redefinition, association specialization, association-class specialization and XOR. Although their standard semantics is ambiguous and their interaction unclear, the UML meta-model intensively uses these constraints. Moreover, some of these interactions have been declared in the UML meta-model as variation points. The paper discusses possible semantics of inter-association constraints (subsets, union, redefinition and association-class specialization), analyzes their interaction, and suggests coherent semantics that minimizes contradictions with the metamodel (association specialization and XOR are left out, due to space limitations). The paper also introduces rules that enforce model correctness. This paper is the first to provide an inclusive analysis of all inter-association constraints.

Finite satisfiability of class diagrams: practical occurrence and scalability of the FiniteSat algorithm

Models lie at the heart of the emerging Model Driven Development (MDD) approach, in which software is developed by repeated transformations of models. Since models are intended as executable specifications, there is a need to provide correctness management on the model level. The underlying hypothesis of this research is that model level tools should be strengthened, to support model elements in a way that would encourage users to take advantage of their features. Furthermore, model transformations should not neglect the translation of model features. This paper explores the practical relevance of detecting Finite Satisfiability problems on the model level. The frequency of occurrence of Finite Satisfiability problems, and the scalability of the efficient FiniteSat algorithm are studied on a set of synthetic class diagrams, created along designed metrics. The contribution of this work is twofold, first in advancing towards creating a benchmark of class diagrams, and second, in the empirical study of the Finite Satisfiability problem.