CS 290C: Formal Models for Web Software Lecture 6: Model Driven Development for Web Software with WebML Instructor: Tevfik Bultan

Model Driven Development (MDD) In MDD approach software development is driven by models –Models are written in a software modeling language such as UML These high level models are systematically translated to concrete implementations Models provide an abstract, implementation platform independent view of the software system

Model Driven Development Software development is a modeling activity –Even if the developers do not use any modeling language they have mental models of the problem and the solution they are developing –These models are then translated to code using the abstractions provided by the programming language MDD adds more layers of abstraction that can be used for modeling both the problem domain and the solution Different aspects of an application can be modeled using different modeling techniques

Separation of Concerns MDD promotes separation of concerns Different modeling techniques are used for modeling different aspects of the application MDD separates technology dependant concerns from the application logic

Automation MDD promotes automation Automated analysis and verification of models –Since models do not contain implementation details they are easier to analyze Automated code generation from models –Guaranteeing conformance to models Runtime monitoring based on models –Using runtime monitoring to make sure that the implementation follows the behavior specified in the model Automated test generation –Models can be used to generate tests for testing the implementation

Model Driven Architecture (MDA) MDA is supported by the Object Management Group (OMG) MDA separates the business and application logic from the underlying implementation platform MDA is a forward engineering approach where first abstract model diagrams are developed which are later transformed to code The goal of MDA is to separate the conceptual design from the implementation architecture

The MDA approach First, the developers build platform independent models for the application –uses machine readable design models –uses modeling languages such as UML These platform independent models document the business functionality of an application –separate from the technology-specific code that implements it After the implementation platform is chosen –the platform independent models are translated to platform specific models –then the platform specific models are used to guide the implementation for the chosen platform

Platform Independance The platform independent models enable the business and technological concerns to evolve separately Models enable interoperability both within and across platform boundaries –models serve as a technology neutral specification of the functionality Different components of the system can be implemented in different platforms –they can be easily integrated since they all conform to the same design models

MDA Benefits for Software Lifecycle Implementation: MDA enables integration of new implementation infrastructures based on the existing design models Integration: Integration is easier since both the implementation and the design models exists at the time of integration. Maintenance: the availability of the design in a machine- readable form gives developers direct access to the specification of the system, making maintenance much simpler Testing and simulation: The design models can be validated against requirements and executable models can also be used to simulated the behavior of the system

Web Modeling Language (WebML) WebML is a modeling language for developing web applications – WebML was proposed about 10 years ago WebML if a modeling language for MDD of web applications WebML models are high-level, implementation- independent, conceptual models

WebML References Stefano Ceri, Piero Fraternali, Aldo Bongio: Web Modeling Language (WebML): a modeling language for designing Web sites. Computer Networks 33(1-6): (2000) Stefano Ceri, Piero Fraternali, Maristella Matera: Conceptual Modeling of Data-Intensive Web Applications. IEEE Internet Computing 6(4): (2002) Stefano Ceri, Marco Brambilla, Piero Fraternali: The History of WebML Lessons Learned from 10 Years of Model-Driven Development of Web Applications. Conceptual Modeling: Foundations and Applications 2009: Stefano Ceri et al. Designing Data-Intensive Web Applications, Morgan Kaufmann Series in Data Management Systems.

WebML and WebRatio There is a spinoff company that has a software tool that generates code from WebML models – WebML models can be translated to implementations using a software tool based on WebML called WebRatio Separation of concerns –Technological mapping is handled by WebRatio and WebML models are platform independent

WebML WebML is used to create orthogonal conceptual models: –Data model Entity-relationship diagrams (UML class diagrams), describes the data schema –Navigation model Modeling of how information is assembled to pages and linked to each other (hypertext model) –Presentation model Modeling of the views, page layout Separation of concerns: data content, interface logic and presentation logic are specified separately

Data Model The data model is consists of entity-relationship diagrams –similar to UML class diagrams Identify the data objects that will be stored in the back-end database –The attributes of the data objects –The relations among the data objects

Navigation Model (Hypertext Model in WebML) Units for publishing content: –Data and index units Links –Navigation links –Transport links (no navigation, just parameter passing between units) –Automatic links (automatically navigated) Contextual links transfer data whereas non-contextual links only used for navigation The semantics of navigation model is based on statecharts –There is a page navigation algorithm which given a WebML navigation model and a user event identifies what the contents of the next page will be

Presentation Model Enables dressing of the hypertext model to obtain web pages with the desired layout and the look & feel It allows the use of html templates which are applied to the hypertext model to generate the pages WebML includes pre-defined presentation style sheets that can be used

Modeling skeleton Using WebML it is possible to abstract a web application to elementary structures called skeletons (pairs of data and hypertext models) that show a certain aspect of the design Core skeletons for displaying and managing business objects Access skeletons for categorizing and selecting concepts Interconnection skeletons define the relations between the business objects Content management skeletons