The Role of Patterns in Modern Software Engineering

The Role of Patterns in Modern Software Engineering Markus Völter voelter@acm. org www. voelter. de . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering About me • • Independent Consultant • Focus on • Software Architecture • Middleware • Model-Driven Software Development Markus Völter voelter@acm. org www. voelter. de Based out of Heidenheim, Germany . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering CONTENTS • • Introduction Describing challenges of systems in certain domains Describing the structures of certain kinds of systems Describing interesting aspects of new paradigms Use of Patterns in Tools Writing your own patterns Using Patterns to Architect Systems Summary . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering CONTENTS • • Introduction Describing challenges of systems in certain domains Describing the structures of certain kinds of systems Describing interesting aspects of new paradigms Use of Patterns in Tools Writing your own patterns Using Patterns to Architect Systems Summary . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Introduction • • Today patterns are not a hype anymore. Patterns themselves are not a selling point anymore – what counts is the actual content. • A while ago, any book with “patterns” on it sold well • Today, there are books on certain topics that use the notion of patterns to make their point: • Evans: Domain-Driven Development • Binder: Testing Object-Oriented Systems • • I think this is good. Patterns have become a tool for the software developer, comparable to programming languages: very important, but nobody makes a fuzz about them (anymore) • And in both areas, there are exceptions . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering CONTENTS • • Introduction Describing challenges of systems in certain domains Describing the structures of certain kinds of systems Describing interesting aspects of new paradigms Use of Patterns in Tools Patterns as a form of literature Using Patterns to Architect Systems Summary . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Well-Known complex technical domains • Patterns are used do document well-known solutions in domains have been worked on in IT for a long time. • Examples include • Distributed Objects Systems [POSA 2] • Resource Management [POSA 3] • Patterns of Enterprise Application Architecture [Po. EAA] • Enterprise Integration Patterns [EIP], Integration Patterns [IP] • As of their nature, these patterns are interesting to a large number of developers; thus, they are typically documented in book form. . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Well-Known functional domains • Also, functional domains use patterns for documenting their best practices. • Some of these patterns aren’t published at all for reasons of competitive advantages • I know of patterns for • Telecoms • Safety-Critical Software • Mobile Phone Infrastructure • … . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering New Technologies • New and promising technologies use patterns to document the experience (of typically few) experienced developers to help others learn the topic – and thus spread the new technology • Examples include • Model-Driven Software Development [MDSD] • Aspect-Oriented Software Development [AOP, AOP-MDSD] • You’ll find those patterns typically in the proceedings of patterns conferences, or at the conferences for the respective technologies (AOSD). . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering How to use in Software Engineering…? • For people who work in the respective domain or with the respective technology, the patterns help to solve certain key problems they might stumble about when working in the domain. • For newbies who want to “get into” the respective domain or technology the patterns help to understand the structure, challenges, key issues and proven solutions; i. e. the patterns help learning to master the domain . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering CONTENTS • • Introduction Describing challenges of systems in certain domains Describing the structures of certain kinds of systems Describing interesting aspects of new paradigms Use of Patterns in Tools Writing your own patterns Using Patterns to Architect Systems Summary . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Inner Structures of complex Systems • Pattern Languages are collections of patterns that describe a “whole”, • The overall structure is too complicated to be described in one pattern – thus the language. • Sometimes there alternative sequences through the pattern language describing various alternatives of the “whole” • A pattern language thus describes how to build sich a complex system of a certain type • There are various examples of such pattern languages, • Many cover middleware technology [SCP, REMO] , and • They are published in various forms . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting • Describes the internal architecture of remoting middleware such as CORBA, Web. Services or. NET Remoting [REMO] • It can be seen as a pattern language that describes the internal workings of Broker architectures in industrial practice. . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting II • Basic Remoting Infrastructures . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting III: Server Request Handler • Context: You are providing remote objects in a server application, and invokers are used for message dispatching • Problem: • • The request message has to be received from the network; Managing communication channels efficiently and effectively is essential Network communication needs to be coordinated and optimized Solution: • • • Server request handler deals with all communication issues of a server application: Receives messages from the network Combines the message fragments to complete messages Dispatches the messages to the correct invoker Manages all the required resources (connections, threads, …) . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting IV: Server Request Handler 2 . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting V • Basic Remoting Infrastructures . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting VI • Interactions . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting – Technology Projection; . NET Example . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting - Identification . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting - Lifecycle . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting - Extension . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting – Extended Infrastructure . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: Remoting – Asynchrony . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering How to use in Software Engineering…? • You can use those pattern languages to gain a deep understanding of the respective type of system. • Typically, those PL’s are described in a technologyindependent fashion; so the PL teaches the concepts and principles, and not the technology. • This is necessary in case you may have to build such a system yourself – maybe for an environment (embedded? ) where such technology is not available off-the-shelf. • PL’s also often help to compare different technologies/implementations since they are (usually) technology independent. . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering CONTENTS • • Introduction Describing challenges of systems in certain domains Describing the structures of certain kinds of systems Describing interesting aspects of new paradigms Use of Patterns in Tools Writing your own patterns Using Patterns to Architect Systems Summary . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Interesting Aspects of new paradigms • Patterns are used as a form for describing best practices for using new or emerging paradigms • Aspect Oriented Programming (Arno’s Work) • Patterns for Model-Driven Development (my own) • The well known (often Go. F-Patterns) are used to describe the structure of new Frameworks and tools (such as the Spring framework) . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Example: MDSD Patterns • Collects industry best practices for model-driven software development and MDA; see [MDSD] • They cover • Process issues • Tool architecture • Domain modelling • Application Platform development (transformations, generators) . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering How to use in Software Engineering…? • If you work with the new paradigm, you can use the patterns to get a feel of how this new paradigm can be used efficiently. • You typically don’t find these things in the beginner’s tutorials • Or, if you have a problem with the tool or paradigm, you can use the patterns to find a solution. . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering CONTENTS • • Introduction Describing challenges of systems in certain domains Describing the structures of certain kinds of systems Describing interesting aspects of new paradigms Use of Patterns in Tools Writing your own patterns Using Patterns to Architect Systems Summary . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Use of Patterns in Tools • Tool support for patterns in mainly relevant for modelling, transformation and code generation tools. • There are various forms of how patterns can be used in tools, however, all have the following aspects in common: • The pattern is reduced to it’s “solution UML diagram”. • The tools never consider applicability, consequences and the forces. • It’s up to the tool users (or, in the case of generators) of the tool designers to decide which pattern to use when. . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Use of Patterns in Tools: Classical UML Tools • You can select a pattern from a patterns’ palette. • Typically, the GOF patterns are supported, as well as a couple of technology-specific ones. • You then define which model elements play which of the pattern’s role. • The tool then “implementes” the pattern by • Creating additional model elements, • Modifying the role players according to the pattern’s role definitions . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Use of Patterns in Tools: Simple MDA Tools • The term “pattern” is used here more in the sense of template, i. e. a template that defines how to “expand” a certain model element to another one. • This is relevant specifically in the PIM to PSM transformation world, where (simple) expansion patterns define the transformation • i. e. a UML class stereotyped “Entity Bean” is expanded into a Class with stereotype “Seployment Descriptor”, “Remote Interface” and “Bean Implementation” . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Use of Patterns in Tools: Code Generators • In code generators, the generated code has to be structured reasonably • people have to use it for debugging • It has to perform acceptably • Sometimes it has to be runtime-flexible • So, the well known patterns are used in the generated code. • The generator developer decides about a pattern’s use. • In most cases the use of the pattern is not visible in the generator input (i. e. the model) . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Use of Patterns in Tools: Domain-Specific Languages • Sometimes it is necessary to let the generator user (i. e. the application developer) choose whether to use a certain pattern, or at least specify how to use the pattern. • Often these patterns aren’t really patterns, but rather certain structures and behavior defined in the metamodel • In that case you will not expose the patterns implementation structure to the model (generator input) layer. • Rather you use specific notations in the model to denote the pattern’s use (tags, stereotypes, UML 2 collaborations). . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering How to use in Software Engineering…? Tool Kind Is this useful? Should it be used in SWEngineering? Classical UML Tools Not very useful, since the “pattern meta information” gets lost – you usually cannot easily reverse the pattern’s application If you want to generate code from that, why do you want to see all the details in your model? Simple MDA Tools Not very useful, since non-trivial transformations cannot be expressed by simple template/pattern expansion. Specifically, a query mechanism is missing Code Generators Very useful, the quality of the generated code improves. Often, it also helps to simplify the generator design DSLs Very useful, it helps to make the DSLs more understandable and brief . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering How to use in Software Engineering…? cont‘d • In all cases be advised that you rather use the pattern solution. Patterns, however, are much more: • Context, applicability, forces, consequences, etc. • All these things typically get lost when a pattern is supported in tools. . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering CONTENTS • • Introduction Describing challenges of systems in certain domains Describing the structures of certain kinds of systems Describing interesting aspects of new paradigms Use of Patterns in Tools Writing your own patterns Using Patterns to Architect Systems Summary . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Use of Patterns in Tools: Code Generators • If you come up with certain recurring best practices in your domain (technical or functional) you may want to write these down as patterns. • The pattern forms (there are various forms) all have in common that they require the author to structure the content very strictly. • This forces the author to think hard about stuff such as applicability, forces or consequences • For readers, well-structured content becomes easier to comprehend . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering How to use in Software Engineering…? • Writing things up in pattern form improves the effectiveness of communication, provides a means to break down complex structures and generally improves writing style. • Once you’re accustomed to the patterns form, you will use it implicitly when writing any kind of technical documentation, i. e. • Start by setting the context, • Explain when and for who the following stuff is interesting • Describe the problem and the solution • And then elaborate on the consequences. • Finally, you’ll point to related material . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering CONTENTS • • Introduction Describing challenges of systems in certain domains Describing the structures of certain kinds of systems Describing interesting aspects of new paradigms Use of Patterns in Tools Writing your own patterns Using Patterns to Architect Systems Summary . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Architectural Patterns • Architectural patterns can be used to describe wellworking architectural styles and blueprints. • Many have been described in the POSA series books, for example, specifically in [POSA 1]. • Examples include • Blackboard • Pipes and Filters • Microkernel • Components & Connectors . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering How to use in Software Engineering…? • Architictural Patterns serve as fix points in the design space of an architecture. • You understand the requirements • You design an initial architecture • You find it resembles a certain architectural pattern • You analyze the differences. Are they essential? • You then use the patterns consequences to see if they are acceptable. • Then you may want to iterate… until you maybe hit another pattern in the architectural design space. • When using MDSD, architectural patterns can be used as a basis for architectureal metamodels. • The solution of an architectural patterns can be described as a metamodel. . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering CONTENTS • • Introduction Describing challenges of systems in certain domains Describing the structures of certain kinds of systems Describing interesting aspects of new paradigms Use of Patterns in Tools Writing your own patterns Using Patterns to Architect Systems Summary . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering Summary • Patterns are everywhere. They have moved into many domains and “corners” where you’d not expect them. • Maybe we could summarize: • The less hyped uses of patterns (architecture, writing your own patterns) • are more important than the hyped ones (“our UML tool comes with patterns support”). . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering CONTENTS • • Introduction Describing challenges of systems in certain domains Describing the structures of certain kinds of systems Describing interesting aspects of new paradigms Use of Patterns in Tools Writing your own patterns Using Patterns to Architect Systems Summary THE END. THANK YOU! . ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r

The Role of Patterns in Modern Software Engineering References • • • AOP Arno Schmidmeier, various AOP Patterns, available through www. aspectsoft. de AOP-MDSD Markus Voelter, Patterns for Handling Cross-Cutting Concerns in MDSD, http: //www. voelter. de/data/pub/Models. And. Aspects. pdf EIP Gregor Hohpe, Bobby Woolf; Enterprise Integration Patterns : Designing, Building, and Deploying Messaging Solutions; Addison. Wesley 2003 IP Integration Patterns, Microsoft Corporation, 2004 MDSD Markus Voelter, Patterns for Model-Driven Software Development; http: //www. voelter. de/data/pub/MDDPatterns. pdf Po. EAA Martin Fowler, Patterns of Enterprise Application Architecture, Addison-Wesley 2002 POSA 1 Frank Buschmann, Regine Meunier, Hans Rohnert, Peter Sommerlad, Michael Stal; Pattern. Oriented Software Architecture, Volume 1: A System of Patterns, Wiley 1996 POSA 2 Douglas Schmidt, Michael Stal, Hans Rohnert, Frank Buschmann; Pattern-Oriented Software Architecture, Volume 2, Patterns for Concurrent and Networked Objects; Wiley 2000 POSA 3 Michael Kircher, Prashant Jain; Pattern-Oriented Software Architecture, Volume 3, Patterns for Resource; Management, Wiley 2004 REMO Voelter, Kircher, Zdun; Remoting Patterns; Wiley 2004 SCP Voelter, Schmid, Wolff; Server Component Patterns; Wiley 2002. ingenieurbüro für sof twaretechnologie w w w. vo © 2 0 0 5 M a rk u s V ö l t e r