An Ontology Based Approach for Formal Modeling of Structural Design Patterns

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1 An Ontology Based Approach for Formal Modeling of Structural Design Patterns Ashish Kumar Dwivedi 1, Anand Tirkey 2, Santanu Kumar Rath 3 Department of Computer Science and Engineering National Institute of Technology Rourkela, , Odisha, India shil2007@gmail.com 1, andy9c@gmail.com 2, and skrath@nitrkl.ac.in 3 Abstract The present day, software are becoming too much complex by nature. Hence there is a need for developing the right solution of complex requirements. To solve various design problems, a number of tools and techniques are available, one of them is known as design pattern, which helps to find a better solution for the problems, which are recurring in nature. Generally, the notation of design pattern is often described using UML (Unified Modeling Language), which is semi-formal in nature. The UML notation may lead to ambiguities and inconsistencies. In this study, attempts have been made to model the logics behind of structural design patterns using Web Ontology Language (OWL). For consistency checking of the OWL notation, an ontology reasoner i.e., Pellet has been considered. In order to analyze the composition of design patterns, description logic has been applied. For the evaluation of the presented study, an example i.e., online banking system is used. Index Terms Design patterns, Description Logic, Ontologybased Modeling, OWL, RDF, UML. I. INTRODUCTION Design of present day software very much depends on fixing up its configuration by identifying different architectural elements i.e., components, connectors, and configuration. During the phase of fixing configuration, designer identifies that some aspects get repeated. Hence the role of patterns is observed to help when designer sets principal design decisions to solve recurring design problems. In the past two decades, various software patterns are analyzed [1] [2] [3] [4]. In order to utilize pattern-based solution, details of various tools are discussed in the literature [5]. The pattern-based tools become helpful for the pattern instantiation as well as pattern detection process. The pattern-based solutions are often described by using pattern template elements. Gamma et al. [1] have presented a number of template elements for their design patterns such as creational, structural and behavioral design patterns. In this study, structural design patterns are considered for analyzing the composition of patterns. Structural patterns are mainly concerned with the structure of classes and relationships contained by respective patterns. Each pattern has a set of rules for the composition of pattern s constituents, which are described by template elements such as pattern name, pattern applicability, pattern-based solution, etc. Sometimes, templatebased description becomes ambiguous and inconsistent, which requires further rigorous analysis. During the analysis and design of a pattern-based system, various software pattern are analyzed by using semi-formal notations, which may lead to ambiguities and inconsistencies. Checking the consistency and extendability of patterns allow detecting different design problems at the very early phases of software development process. Formal modeling techniques help to verify and validate the system requirements and provide rigorous analysis of a system at the early phases of the development process [6] [7]. Due to large and complex nature of requirements of software system, number of modeling techniques came into existence. One of them is an ontology based modeling technique, which helps to organize system information in conceptual domains where these information can be categorized in the form of things [8]. These things can be represented as a group of objects, essential, or existential. In this study, an ontology-based modeling framework is presented for rigorously analyzing pattern-based system. The proposed framework helps to represent software design patterns as RDF (Resource Description Framework) document that can be published as resources on the Web. The framework is based on metamodeling approach, which offer formal constructs of pattern-based solution. A metamodel is also known as model of models having a crucial role in standard community such as Object Management Group (OMG) [9]. The concept of ontology provides formal construction for domain formalization by incorporating mathematical logics. For the last decade, ontology and metamodels are developed in parallel isolation [10] [11]. In order to validate the proposed approach, online banking system is considered as a case study. In this scenario, accessing-bank-account usecase is considered where a number of security design problems such as information disclosure, spoofing, denial of service, etc., may occur. These security problems are resolved by applying various security patterns such as SingleAccessPoint, CheckPoint, Authenticator, etc. Security patterns are used in banking operations such as withdrawal, fund transfer, change password, etc. Firstly, structural design patterns are used to solve security problems of a banking system at the design phase. Subsequently, patternbased solutions are analyzed by using Web Ontology Language (OWL) [12]. In order to represent the ontology of structural patterns, an ontology editor i.e. Protégé [13] is being used. At the end of this study, a comparative analysis has been presented between ontology-based modeling of design patterns and other existing formal modeling approaches /16/$ IEEE

2 II. RELATED WORK It is observed that a number of authors have worked mostly on two application areas of ontology, such as either to formalize different software design patterns or to formalize architectural styles using formal modeling notations. Related research works are discussed bellow: Dietrich and Elgar [14] have proposed a novel scheme to formally specify software design patterns. They have ensured that their approach specifies design patterns and their constructs, such as participant classes, relationships, and their instances. Wang et al. [15] have proposed a technique to formally specify and verify feature diagrams by considering Semantic Web technology such as OWL. They have used OWL reasoning engine i.e., FaCT++ for the consistency checking of feature configurations. Parreiras et al. [16] have formalized abstract factory and strategy design patterns by using description logic. They have performed mapping process between OWL and UML for the modeling of abstract factory and strategy pattern. Nicholson et al. [17] have used visual language of codecharts i.e., LePUS3 for specifying and verifying software design patterns. They have presented a set of tool support for analyzing design patterns with codecharts. Chaturvedi and Prabhakar [18] have used the concept of generic ontology as a runtime component in Gamma et al. [1] creational patterns. Further they have analyzed the implementation of the creational patterns and concluded that their proposed solution is not only removes the deficiencies determined in selected patterns, but also provides the patterns reusable. Bayley and Zhu [19] have presented a meta-modeling approach i.e., GEBNF (generalized extended backus-naur form) to the formalization of software design patterns. According to authors, their approach provides formal reasoning about patterns and their composition. Pahl et al. [20] have proposed an ontology-based technique for the analysis of an architectural style. They have considered a meta-level modeling approach, known as Description Logic (DL) for system property specification. They have developed a framework which supports the specification and subsequently provides mathematical model for architectural style. Zhu and Bayley [21] have analyzed the notion of validity of pattern composition. They have proposed a formal method for proving and disproving of the validity of pattern composition. Dwivedi and Rath [22] have formalized the composition of security patterns by using a lightweight formal modeling notation i.e., Alloy. They have conducted a quantitative evaluation of security patterns against the security properties. Tounsi et al. [23] have performed formal modeling of SOA (serviceoriented architecture) design patterns using Event-B. Their approach is based on metamodeling concepts. Dwivedi and Rath [24] have formalized a complex architectural style i.e., C2 (component and connector) using formal method Alloy. Kim et al. [25] have presented a formal approach to specify design patterns which is based on the concept of role. They have considered a metamodeling approach to the formalization of design patterns using a formal method Object-Z. III. PROPOSED WORK Due to growing amount of information, a number of resources are available, which store data and result using different storage method. But the resources do not grow with the same rate as information grow. This type of problem can be solved by considering the concept of Semantic Web [26], which offers data to be shared and reused by various domain. OWL and RDF are components of the Semantic Web. OWL is a language of ontology which is based on formal notations such as FOL (First Order Logic) and DL (Description Logic). In this study, OWL-DL is considered to specify pattern-based system requirements. OWL is represented by three elements, such as Individuals, Properties, and Classes. In this section, an ontology-based pattern modeling framework is presented that is inspired from [14]. Firstly, structural patterns are described by using UML, subsequently it is analyzed by using OWL. A. Ontology-Based Modeling Framework The presented modeling framework is based on the concept of metamodel which enables analysis and design of UML based pattern notations. The presented modeling framework is an extended form of traditional model driven development approach as shown in Figure 1. The framework is a combination of four models such as analysis model, design model, formal model, and code. According to this framework, functional requirements of a system are mapped into analysis model such as usecase model. The analysis model can easily transformed into XMI code by using an Eclipse-based modeling tool. The XMI code of analysis model is transformed into design model. The design model is a UML-based class digram, which is mostly used to express software design patterns. A pattern-based solution is often available in the form of UML class digram which may show an ambiguous and inconsistent representation. Structural design patterns are associated with the framework as to how classes and objects are composed to form a larger structure. UML-based relationships, such as inheritance, aggregation, composition, etc. play an important role for providing pattern-based solution. These relationships should have semantic definition during pattern refinement process. In order to formally specify design pattern notation, it needs to be transformed into formal notation such as OWL-DL which can be mapped into code. B. Analysis of the composition of Structural Design Patterns The proposed study mainly is concerned with design model and formal model in modeling framework. Design model is nothing but a pattern-based solution which is represented using UML class diagram and UML sequence diagram. The patternbased solution represents a composition of patterns which are also known as pattern language [27]. A pattern language is shown as a diagram to represent the actual relationship among patterns. The details of pattern language are presented by Alexander in his book A Pattern Language containing 253 patterns. In order to analyze structural design pattern, a pattern-based solution for an online banking system has been presented.

3 Fig. 1. Ontology based modeling framework for structural design patterns Fig. 2. Pattern composition for Online banking system The present day, user requires greater advocacy, security, and control in their banking system. But they have faced problems in terms of acquiring flexibility, easy to use, align business to technology, etc. These problems can be solved by considering suitable design techniques. In this study, design patterns such as Facade, Proxy, Composite, Adapter, and Command are used to solve the design problems. The structural and behavioral aspects of patterns composition are presented by using UML class diagram and sequence diagram. Figure 2 shows the concept of patterns composition using a case study. In this figure, CheckPoint acts as Facade and SecurePolicy, Authenticator, and Proxy act as subsystems for Facade. In this example, the composition of CheckPoint and SecurePolicy represent Adapter design pattern. The classes, such as User, Command, Withdrawal, Fundtransfer, and PolicyChange are composed in such a way that they represent their functions as a composite design pattern, where Command acts as a Component and PolicyChange acts as a Composite. For using Proxy pattern, CheckPoint acts as a Client and Account act as a RealSubject for Proxy. The dynamic aspect of design of composition of patterns is presented in Figure 3. In this aspect User sends a request to access a resource. This request initially gets verified by security patterns such as Single Access Point, CheckPoint, SecurePolicy, and Authenticator. If User s request gets authenticated, then user tries to access resource through the Proxy. In this system, CheckPoint acts as a Facade structural pattern that calls Proxy pattern to create a new proxy for that request. The created proxy is being provided to the User. User considers accesscommand method that is processed by Command component. It checks access policy rules on the basis of those rules where user accesses the resource i.e., Account. C. Ontology for Structural Design Patterns Ontology provides the conceptualization to software design patterns by providing semantic relationships between pattern classes. In Adapter pattern, Adapter adapts Adaptee to Target by assigning to the concrete class of Adapter; but Adapter won t work when a class and all its subclasses are adapted. Similarly, in Composite pattern, new components can be added and composite class defines behavior for these components for which a client does not have to be changed. These consequences need to be declared in the form of knowledge representation so that designers and developers can understand and utilize the actual semantics of classes, objects, and their relationships. OWL is considered for the formal modeling of structural design patterns definition and its consequences. Generally, design patterns are specified using UML notations, which are semi-formal in nature. Hence, the mapping of UML models into OWL becomes helpful for pattern detection, pattern refinement, pattern instantiation. UML elements, such as package, class, instance, multiplicity, enumeration, property can be mapped into OWL elements, such as, ontology, class, individual, cardinality, objectoneof (and dataoneof), object- Property (and dataproperty) respectively. The OWL representation of structural design patterns is shown in Figure 4.

4 Fig. 3. Behavioral aspect of structural pattern composition for Online banking system Fig. 4. OWL representation of structural design patterns

5 TABLE I PROPERTY SPECIFICATION OF STRUCTURAL DESIGN PATTERNS S. No. DL Notation 1. (StructuralDesignPattern Pattern) 2. ((AdapterDP BridgeDP CompositeDP DecoratorDP FacadeDP FlyweightDP ProxyDP) StructuralDesignPattern) 3. ((((Adapter Adaptee Target) AdapterDP) (Adapter Class (Target Adaptee)) (Adapter Object Target))) 4. (((Adapter Class Adapter Object) Adapter)) 5. ((((Abstraction RefinedAbstraction Implementor ConcreteImplementor) BridgeDP) ((RefinedAbstraction Abstraction) (ConcreteImplementor Implementor) ((1 : Abstraction) (2 : Implementor))))) 6. ((((Component Composite Leaf ) CompositeDP) ((Composite Leaf ) Component))) 7. ((((Component Decorator ConcreteComponent ConcreteDecorator) DecoratorDP) ((ConcreteComponent Component) (ConcreteDecorator Decorator)))) 8. ((((Facade SubSystem) FacadeDP) (SubSystem Facade))) 9. ((((FlyweightFactory Flyweight ConcreteFlyweight) FlyweightDP) ((ConcreteFlyweight Flyweight) ((1 : FlyweightFactory) (2 : Flyweight ))))) 10. ((((Proxy Subject RealSubject) ProxyDP) ((RealSubject Proxy) Subject))) 11. (Adapter Instance createinstanceof.adaptee) Figure 4 represents patterns, subpatterns, classes and sub- Classes of structural design patterns. Structural design patterns contain subpatterns, such as Adapter, Bridge, Composite, Decorator, Flyweight, and Proxy. Similarly, these subpatterns contain classes and subclasses, also known as participants. For example Adapter contains four participants, such as Adapter, Adaptee, Target, and Client. Bridge contains Implementor and Abstraction as classes and ConcreteImplementor and RefinedAbstraction as subclasses. Composite also contains four participants, such as Component, Client, Leaf, and Composite, where Leaf and Composite are subclasses of a class Component. Decorator contains Component, ConcreteComponent, and ConcreteDecorator as pattern participants. Facade contains two participants, such as Facade and subsystem classes. Flyweight contains five participants, such as FlyweightFactory, Client, Flyweight, ConcreteFlyweight, and UnsharedConcreteFlyweight. ConcreteFlyweight and UnsharedConcreteFlyweight are subclasses of a class Flyweight. These subclasses are different in terms of implementation for state sharing of objects. A ConcreteFlyweight object must be sharable, whereas not all Flyweight subclasses need to be shared for UnsharedConcreteFlyweight. Proxy contains three participants, such as Subject, RealSubject, and Proxy, where Proxy and RealSubject are subclasses of Subject. In this study, an ontology is presented for the structural design patterns that specifies number of object properties, data properties, axioms, annotation properties, individuals, etc. The object properties represented for this ontology are subpatternof, isparticipantof, isinheritedfrom, ispartof, create etc. The data propeties are sharedstate, unsharedstate, isleaf etc. Protégé is an ontology editor which is easily available in the form of plugins. OWL-Viz is a tool integrated with Protégé that helps to visualize different classes and their relationships. Protégé supports DL-Query tab, that is used to execute DLquery with the help of OWL reasoner i.e., Pellet. Property specification of structural design patterns is performed by using description logic. D. Property Specification of Structural Design Patterns using Description Logic Description logic is a form of mathematical logic mainly used for formal representation of knowledge languages. Description logic formalizes different domains with the help of concepts and relationships which are represented as classes and relations respectively. It is similar to first order logic (FOL) added with some other notations. Description logic supports a number of mathematical operators, such as and ( ), or ( ), not ( ), subset-of ( ), equivalent ( ), model ( =), greater-or-equal ( ), less-or-equal ( ) etc. for analyzing the properties of a system requirements [28]. Description logic also supports existential quantifier ( ) and universal quantifiers ( ). Two special operators, such as ( ) and ( ) supported by DL denote the meaning having all individuals and no individual respectively. DL notations presented in Table I shows the formal relation and sensitive axioms for the structural design patterns. The DL notation is helpful to specify UML class diagram. For example, generalization can be specified by using operator. In a Flyweight design patterns, FlyweightFactory is a containing class and Flyweight is an aggregate class which are specified as ((1 : FlyweightFactory) (2 : Flyweight )) using DL notations. In AdapterDP, Adapter creates an instance of Adaptee, which is specified as Adapter Instance createinstanceof.adaptee. The presented DL notations are verified by using an OWL reasoner i.e., Pellet. E. Comparison In order to assess the performance of ontology-based modeling, a comparative analysis has been made with existing approaches as shown in Table II. Five parameters such as modeling language, tools, logic, UMLtoFM, and code generation are considered for the comparison. OWL notation is compared with LePUS3, Object-Z, Event-B, Alloy, and GEBNF which are presented in related work section. UMLtoFM represents transformation of UML notation into respective formal methods. Existing approaches are based on metamodeling concept

6 and uses FOL (first order logic), whereas OWL uses both FOL and DL. OWL helps for the refinement of design patterns. In this study, pattern refinement is described by specifying inheritance relationship. Because in structural design patterns, candidate classes of a particular patterns are often considered inheritance to organize interfaces. The main benefit of OWL it to model design document as a web content using RDF. Representing the design patterns in the form of OWL/RDF enables user to deploy the pattern definitions on the web servers. TABLE II COMPARISON BETWEEN OWL AND EXISTING TECHNIQUES S. No. Modeling Code Tools Logic UMLtoFM Language Generation 1. LePUS3 TTP Toolkit FOL No No 2. Object-Z Z/EVES FOL Yes No 3. Event-B Rodin FOL No Yes 4. Alloy Alloy Analyzer FOL Yes No 5. GEBNF No FOL No No 6. OWL Protégé FOL, DL Yes Yes IV. CONCLUSION AND FUTURE WORK The presented study offers an ontology-based approach for modeling and specification of structural design patterns. In this study, an attempt has been made to formalize the representation and composition of software design patterns as a knowledge representation using Web Ontology Language. Various design patterns are being analyzed by considering formal notations, such as Object-Z, Event-B, EBNF, etc. These formal modeling languages have certain limitations in terms of requirement specification and tool support. The proposed scheme utilizes the concept of ontologies in the field of software engineering by specifying UML notation using Description Logic. This approach is helpful to understand the reusability and extendability of the modeling of complex applications. Ontology-based formal modeling confirms the consistency, unambiguity, and understandability related to the complexity and decidability of the required application in the area of software specification and design. It is hereby proposed to extend the application of ontologies in other areas in future, such as modeling of behavioral design patterns and security patterns. REFERENCES [1] E. Gamma, R. Helm, R. Johnson, and J. Vlissides, Design patterns: Elements of Reusable Object-Oriented Software. Addison-Wesley, [2] A. K. Dwivedi and S. K. Rath, Incorporating security features in service-oriented architecture using security patterns, ACM SIGSOFT Software Engineering Notes, vol. 40, no. 1, pp. 1 6, [3] M. Fowler, Patterns of enterprise application architecture. Addison- Wesley, Boston, USA, [4] P. Pradhan, A. K. Dwivedi, and S. K. Rath, Detection of design pattern using graph isomorphism and normalized cross correlation, in Contemporary Computing (IC3), 2015 Eighth International Conference on. IEEE, 2015, pp [5] M. Zanoni, F. A. Fontana, and F. Stella, On applying machine learning techniques for design pattern detection, Journal of Systems and Software, vol. 103, pp , [6] J. Woodcock, P. G. Larsen, J. Bicarregui, and J. Fitzgerald, Formal methods: Practice and experience, ACM Computing Surveys (CSUR), vol. 41, no. 4, pp. 1 36, [7] A. K. Dwivedi and S. K. Rath, Selecting and formalizing an architectural style: A comparative study, in Contemporary Computing (IC3), 2014 Seventh International Conference on, Aug 2014, pp [8] Y. Zhao, J. Dong, and T. Peng, Ontology classification for semanticweb-based software engineering, IEEE Transactions on Services Computing, vol. 2, no. 4, pp , Oct [9] OMG, Object management group, [10] B. Henderson-Sellers, Bridging metamodels and ontologies in software engineering, Journal of Systems and Software, vol. 84, no. 2, pp , [11] D. Dermeval, J. Vilela, I. I. Bittencourt, J. Castro, S. Isotani, P. Brito, and A. Silva, Applications of ontologies in requirements engineering: a systematic review of the literature, Requirements Engineering, pp. 1 33, [12] M. Dean and G. Schreiber, Web ontology language, org/tr/owl-ref/, [13] Protégé, Description is available from, products.php#desktop-protege, [14] J. Dietrich and C. Elgar, Towards a web of patterns, Web Semantics: Science, Services and Agents on the World Wide Web, vol. 5, no. 2, pp , [15] H. H. Wang, Y. F. Li, J. Sun, H. Zhang, and J. Pan, Verifying feature models using OWL, Web Semantics: Science, Services and Agents on the World Wide Web, vol. 5, no. 2, pp , [16] F. S. Parreiras, S. Staab, and A. Winter, Improving design patterns by description logics: A use case with abstract factory and strategy. in Modellierung 2008, vol. P-127 of LNI, 2008, pp [17] J. Nicholson, A. H. Eden, E. Gasparis, and R. Kazman, Automated verification of design patterns: A case study, Science of Computer Programming, vol. 80, pp , [18] A. Chaturvedi and T. Prabhakar, Ontology driven creational design patterns as parameterized and reusable components, ACM SIGAPP Applied Computing Review, vol. 14, no. 1, pp. 6 19, [19] I. Bayley and H. Zhu, Formal specification of the variants and behavioural features of design patterns, Journal of System and Software, Elsevier, vol. 83, no. 2, pp , Feb [Online]. Available: [20] C. Pahl, S. Giesecke, and W. Hasselbring, Ontology-based modelling of architectural styles, Information and Software Technology, vol. 51, no. 12, pp , Dec [Online]. Available: http: //dx.doi.org/ /j.infsof [21] H. Zhu and I. Bayley, On the composability of design patterns, Software Engineering, IEEE Transactions on, vol. 41, no. 11, pp , [22] A. K. Dwivedi and S. K. Rath, Formalization of web security patterns, INFOCOMP Journal of Computer Science, vol. 14, no. 1, pp , [23] I. Tounsi, M. Hadj Kacem, A. Hadj Kacem, and K. Drira, A refinementbased approach for building valid SOA design patterns, International Journal of Cloud Computing 2, vol. 4, no. 1, pp , [24] A. K. Dwivedi and S. K. Rath, Analysis of a complex architectural style c2 using modeling language alloy, Computer Science and Information Technology, vol. 2, no. 3, pp , [25] S.-K. Kim and D. Carrington, A formalism to describe design patterns based on role concepts, Formal aspects of computing, vol. 21, no. 5, pp , [26] T. Berners-Lee, Semantic web, [27] M. Hafiz, P. Adamczyk, and R. E. Johnson, Growing a pattern language (for security), in Proceedings of the ACM International Symposium on New Ideas, New Paradigms, and Reflections on Programming and Software, ser. Onward! 12. New York, NY, USA: ACM, 2012, pp [Online]. Available: [28] S. Rudolph, Foundations of description logics, in Reasoning Web. Semantic Technologies for the Web of Data. Springer, 2011, pp