Markus Völter voelter@acm voelter.de

Model-DrivenSoftware Development www.mdsd-buch.de Some Essential Best Practices Markus Völtervoelter@acm.orgwww.voelter.de

About me Markus Völter voelter@acm.org www.voelter.de • Independent Consultant • Based out of Heidenheim, Germany • Focus on • Software Architecture • Model-Driven SoftwareDevelopment • Middleware

Before we start… I • Model-Driven Software Development is about making software development more domain-related as opposed to computing related. It is also about making software development in a certain domain more efficient.

Before we start … II: MDSD on a Slide several Metametamodel target subdomains software software designexpertise architecture architecture bounded area of partial knowlege/interest composable multiple knowledge viewpoint multi-step transform Domain single-step compile semantics Model Ontology interpret no precise/ Domain roundtrip executable Specific Language graphical Metamodel textual

Before we start … III: MDSD and MDA • Focus: Platform Independence, (Tool) Interop MOF several Metametamodel target software software subdomains architecture architecture designexpertise bounded area of partial knowlege/interest composable PIM, PSM, .... QVT multiple viewpoint multi-step transform Domain single-step compile semantics Model Ontology interpret no precise/ Domain roundtrip executable Specific OCL, Action Semantics Language UML+Profiles graphical Metamodel textual

C O N T E N T S • Domain Architecture • Domain Metamodelling • Code Generation • Tools • Features And Structure • An Example • Process • Multi Model • Architecture and CBD • Adopting MDSD Model-DrivenSoftware Development www.mdsd-buch.de Best Practices

How do I come up with a good metamodel? • Incrementally! • Based on experience from previous projects, and by „mining“ domain experts. • A very good idea is to start with a (typically) very well known domain: the target software architecture (platform) Architecture-Centric MDSD

Talk Metamodel • In order to continuously improve and validate the FORMAL META MODEL for a domain, it has to be exercised with domain experts as well as by the development team. • In order to achieve this, it is a good idea to use it during discussions with stakeholders by formulating sentences using the concepts in the meta model. • As soon as you find that you cannot express something using sentences based on the meta model, • you have to reformulate the sentence • the sentence’s statement is just wrong • you have to update the meta model.

Talk Metamodel II • Example: • A component owns any number of ports. • Each port implements exactly one interface. • There are two kinds of ports: required ports and provided ports. • A provided port provides the operations defined by its interface. • A required port provides access to operations defined by its interface.

Leverage the Model • The information captured in a model should be leveraged to avoid duplication and to minimize manual tasks. • Hence you may generate much more than code: • user guides • help text • test data • build script • content, etc. • Find the right balance between the effort required for automating manual tasks and the effort of repetitively performing manual tasks • Make use of SELECT FROM BUY, BUILD, OR OPEN SOURCE in your assessment.

Separate Generated and Non-Generated Code • Keep generated and non-generated code in separate files. • Never modify generated code. • Design an architecture that clearly defines which artifacts are generated, and which are not. • Use suitable design approaches to “join” generated and non-generated code. Interfaces as well as design patterns such as factory, strategy, bridge, or template method are good starting points.

Separate Generated and Non-Generated Code II • A) Generated code can call non-generated code contained in libraries • B) A non-generated framework can callgenerated parts. • C) Factories can be used to „plug-in“ the generated building blocks • D) Generated classes can also subclass non-generated classes. • E) The base class can also contain abstract methods that it calls, they are implemented by the generated subclasses(template method pattern)

Produce Nice-Looking Code … whenever possible! • PRODUCE NICE-LOOKING CODE … WHEREVER POSSIBLE! • When designing your code generation templates, also keep the developer in mind who has to – at least to some extent – work with the generated code, for example • When verifying the generator • Or debugging the generated code • Using this pattern helps to gain acceptance for code generation in general. • Examples: • Comments • Use pretty printers/code formatters • Location string („generated from model::xyz“)

Tools: Overview • Many kinds of tools can be used in the context of model driven development: • UML modelling tools • Metamodelling environments • (XMI) Repositories • Code Generators • Model verifiers • There is also a large amount of tools that are „MDA certified“. These range from completely integrated environments such as ArcStyler to simple code generators or technology specific generators (e.g. for J2EE).

Tools: Vendor Lock-in • Because a lot of issues are not yet standardized, it is hard to integrate tools. Open issues include: • Some XMI aspects • Specification of model transformation rules • Code generation • ... • As a consequence, integrated MDD/MDA tooling is currently impossible to achieve without vendor lock-in. • Alternatively, building/integrating your own tooling based on open source can be done, but requires compromises. • Many tools are exemplified in the context of code generation (see other presentation). Build Tools are also important. UML tools (such as Rational XDE) also develop in the direction of supporting MDA.

Tools: The Ideal One • MOF Based Metamodelling, including OCL • Usage of thses metamodels for subsequent modeling of M1 • Metamodel specific repositoriy • GUI adapted to metamodel • Model Validation based on metamodel • Also including OCL • Transformation rules based on user-defined metamodels • Flexible Code Generation • Test support

Implement the Metamodel • Implement the meta model in some tool that can read a model and check it against the meta model. • This check needs to include everything including declared constraints. • Make sure the model is only transformed if the model has been validated against the meta model. • The meta model implementation is typically part of the transformation engine or code generator since a valid model is a precondition for successful transformation.

Ignore Concrete Syntax • Define transformations based on the source and target meta models. • The transformer uses a three phase approach: • first parse the input model into some in-memory representation of the meta model (typically an object structure), • then transforms the input model to the output model (still as an object structure) • and finally unparse the target model to a concrete syntax

Transformations as first class citizens • Transformations (and Templates) are central assets in MDSD. You should treat them accordingly. • Transformations should be versioned. • Refactor transformations to keep them current and well organized. • Modularize transformations, e.g. using object-oriented concepts such as encapsulation, polymorphism, inheritance, etc.

Modular, Automated Transforms • In order to more easily reuse parts of a transformation, it is a good idea to modularize a transform. • Note that in contrast to the OMG, we do not recommend looking at, changing or marking the intermediate models. • They are merely a standardized format for exchangingdata among the transformations. • Example: Multi-Step transformation from a banking-specific DSL to Java via J2EE

External Model Markings (AO-Modelling) • In order to allow the transformation of a source model into a target model (or to generate code) it is sometimes necessary to provide “support” information that is specific to the target meta model. • Example: Entity Bean vs. Type Manager • Adding these to the source model “pollutes” the source model with concepts specific to the target model. • MDA proposes to add “model markings”, but this currently supported well by only very few tools. • Instead, we recommend keeping this information outside of the model (e.g. in an XML file); the transformation engine would use this auxiliary information when executing the transformations.

Example Tool: openArchitectureWare Generator • Open Source, quite active projecthttp://www.openarchitectureware.org • Core Features: • Can Read any model (XMI from various UML tools, UML, textual, JDBC, Java classes …) • Can generate any kind of output • Explicit Domain-Metamodel (implemented in Java) • Semi-Declarative Metamodel Constraints, „Functional Programming“ • Simple, efficient template language • Template Polymorphism and Template overwriting • Multi-Model (Merging-Support)

Example Tool: openArchitectureWare Generator • Core Features cont‘d: • Inter-Model References among various model syntaxes (i.e. UML to XML) • Support for Aspects in the metamodel and in the templates • Arbitrary Namespace Models can be supported • Plugin-Based Generator configuration (ant-based) • Additional Features: • Syntax-Highlighting Template Editor for Eclipse • Metamodel can be generated from UML model, incl. DTD, HTML Docs, etc. • Graphical GEF-Based Editors can be generated • Dialog-Based Editors can be generated • Framework for building IDEs based on this Generator • Future Features • EMF Integration, Visio Integration

Example Tool: openArchitectureWare Generator • How it works:

Example Tool: openArchitectureWare Generator • Usage Examples • Web Development (J2EE, Servlets, Struts) • Banking, Insurances • Mobile Phone Software (C++ + QT, J2ME + Java) • Embedded Software (C, CANbus, Osek) • Automotive Component Middleware • (Interactive) Web sites • Architectural Management, „Entertainment) • Multi-Platform Middleware (XML, C++, Java, …) • Radioastronomy

Teaming issues • Using DSLs is not very different from “normal” programming – every developer can basically do it. • Defining DSLs is, however, something completely different: • Finding the „right“ abstractions, defining metamodels, keeping the various metalevels sorted, etc. is not everybody‘s business. • Some of the tools to define metamodels, DSLs, generators and model-2-model transformations are not (yet) intuitively usable. • Therefore I recommend to keep DSL/generator development to a limited group of people in your project.

Iterative Dual Track Development • Develop Domain Architecture and at least one application at the same time. • Establish rapid feedback from application developers to domain architecture developers. • Develop both aspects iteratively and incrementally. Use strict timeboxing. • Infrastructure develops iteration n+1 whereas application developers use iteration n. • Introduce new Domain Architecture releases only at the beginning of iterations.

Extract the Infrastructure • Before startingITERATIVE DUAL-TRACK DEVELOPMENT, Extract the transformations from manually developed application. • Either, start by developing this prototype conventionally, then build up the MDSD infrastructure based on this running application, • Or extract the code from applications developed in the respective domain before doing MDSD (but only if the quality is sufficiently good!)

One DSL is not enough • Most systems can be structured into various • partitions: functional subsystems • subdomains: technical aspects • It is hardly possible to describe each of these with the same DSL. • You will need to come up withseparate DSLs • … that have to be „connectable“in order to build the complete system

One DSL is not enough II - Example

Rich Domain-Specific Platform • Define a rich domain-specific application platform consisting of • Libraries • Frameworks • base classes • interpreters, etc. • The transformations will “generate code” for this domain-specific application platform. • As a consequence, the trans-formations become simpler. • DSLs and Frameworks are two sides of the same coin

Software Architecture Process „on a slide“ …and actually, this is a talk of its own… • Today‘s Problems: • Too much technology • Too many hypes and buzzwords • Too many standards too early • So: People don‘t focus on architectural concepts • PHASE 1: Elaborate! • Technology-Independent Architecture • Programming Model • Technology Mapping • Mock Platform • Vertical Prototype • PHASE 2: Automate! • Architecture Metamodel • Glue Code Generation • DSL-based Programming Model • Model-based Architecture Validation

MDSD and CBD – the three viewpoints • Type Model: Components, Interfaces, Data Types • Composition Model: Instances, “Wirings” • System Model: Nodes, Channels, Deployments

Component Implementation • Componentimplementation should be based on notationsspecific to the “kind of component” • Various other implementationstragies can be used, such as: • Rule-Engines • “Procedural” DSLs or action semantics • Note that, here, interpreters can often be used sensibly instead of generating code!

Aspect Models • Often, the described three viewpoints are not enough, additional aspects need to be described. • These go into separateaspect models, each describinga well-defined aspect of the system. • Each of them uses a suitable DSL/syntax • The generator acts as a weaver • Typical Examples are • Persistence • Security • Forms, Layout, Pageflow • Timing, QoS in General • Packaging and Deployment • Diagnostics and Monitoring

Adopting MDSD – prerequisites • Well-practices MDSD builds on several mature other practices, among them • Well-defined software architecture • Iterative software development and requirements management • Mature project automation (regression testing, automatic builds, etc.)

Adopting MDSD – process

Levels of MDSD • You would typically start with architecture-centric MDSD where the abstractions of the DSL correspond to the core concepts of the technical platform. • This automates many aspects of the technical aspects; • Results in a wide platform/infrastructure • Many projects can be handled with the infrastructure • In later phases, functional MDSD infrastructures will be built on this technical one, resulting in cascaded MDSD.

Levels of MDSD

Levels of MDSD III – M2M Transformations

Levels of MDSD III – M2M Transformations II

Levels of MDSD III – M2M Transformations III

Markus Völter voelter@acm voelter.de