AM

Besoin

Définir des processus de développement logiciel légers et plus réactifs que prédictifs.

Analyse

Le but de l'AM est de renverser les priorités habituelles, en privilégieant :

• les individus et les interactions plutôt que les processus et les outils ;
• le travail sur le logiciel plutôt qu'une documentation détaillée ;
• la collaboration avec le client plutôt que la négociation de contrat ;
• la réactivité au changement plutôt que le suivi d'un planning établi ;

L'AM réunit un ensemble de :

• Valeurs
  • Communication : Les modèles promeuvent la communication entre votre équipe et MOA comme entre les développeurs de votre équipe.
  • Simplicité : Les modèles sont critiques pour simplifier le logiciel comme le processus de développement — il est plus facile d'explorer une idée, et de l'améliorer alors que votre compréhension s'améliore, en dessinant un diagramme ou deux au lieu d'écrire des dizaines voire même des centaines de lignes de code.
  • Retour (feedback) : L'optimisme est un mal de la programmation, le retour est le traitement. En communiquant vos idées au travers de diagrammes, vous obtenez un retour rapide, vous permettant d'agir sur la base de ces conseils.
  • Courage : Prendre des décisions importantes comme changer de direction quitte à perdre ou réécrire votre travail lorsque vos décisions se révèlent avoir été innapropriées ;
  • Humilité : Ne pas penser tout connaître, et reconnaître que les autres développeurs, les clients, et l'ensemble des parties impliquées dans un projet ont leurs propres domaines de compétences et une valeur à apporter au projet. Chacun à une valeur égale sur le projet et doit être traité avec le même respect.
• Principes :
  • Supposez la simplicité. Lorsque vous développez, vous devez supposer que la solution la plus simple est la meilleure. Ne sur-construisez pas votre logiciel, ou dans le cas d'AM ne dépeignez dans vos modèles pas des fonctionnalités supplémentaires dont vous n'avez pas besoin aujourd'hui. Ayez le courage that you don't need to over-model your system today, that you can model based on your existing requirements today and refactor your system in the future when your requirements evolve. Keep your models as simple as possible.
  • Accepter le changement. Les besoins comme la compréhension des besoins évoluent au cours du temps. La MOA peut les faire évoluer alors que votre projet avance, de nouvelles personnes peuvent arriver et d'autres peuvent partir. La MOA peut tout aussi bien changer son point de vue, modifiant ainsi potentiellement les objectifs et les critères de succès de votre effort. The implication is that your project's environment changes as your efforts progress, and that as a result your approach to development must reflect this reality.
  • Permettre le prochain effort est votre second but. Votre projet peut être considéré comme un échec même si vous livrez un système qui fonctionne – une partie de la réponse aux besoins de la MOA est de s'assurer que votre système est suffisament robuste pour être étendu par la suite. Comme Alistair Cockburn aime à le dire, lorsque vous jouez au jeu du développement logiciel, votre second but est de préparer la prochaine partie. Ce prochain effort pourra être la prochaine version majeure du système plus simplement les opérations et le support de la version que vous êtes en train de réaliser. To enable it you will not only want to develop quality software but also create just enough documentation and supporting materials so that the people playing the next game can be effective. Factors that you need to consider include whether members of your existing team will be involved with the next effort, the nature of the next effort itself, and the importance of the next effort to your organization. In short, when you are working on your system you need to keep an eye on the future.
  • Changement incrémental : Un concept important à comprendre à propos de la modélisation est que vous n'avez pas à trouver la bonne dès la première fois ; en fait, il très improbable que vous puissiez le faire même en essayant. Furthermore, you do not need to capture every single detail in your models, you just need to get it good enough at the time. Instead of futilely trying to develop an all encompassing model at the start, you instead can put a stake in the ground by developing a small model, or perhaps a high-level model, and evolve it over time (or simply discard it when you no longer need it) in an incremental manner.
  • Maximiser l'implication de la MOA. La MOA investit dans des ressources - temps, argent, logistique, etc. - pour obtenir un logiciel qui répond à ses besoins. Stakeholders deserve to invest their resources the best way possible and not to have resources frittered away by your team. Furthermore, they deserve to have the final say in how those resources are invested or not invested. If it was your resources, would you want it any other way?
  • Modéliser dans un but : De nombreux développeurs sont attentifs à ce que leurs artefacts - modèles, code source ou documents - soient suffisament détaillés, pas trop détaillés, ou suffisament précis. Ce qu'ils ne font pas est de prendre du recul et se demander pourquoi et pour qui ils créent cet artefact. With respect to modeling, perhaps you need to understand an aspect of your software better, perhaps you need to communicate your approach to senior management to justify your project, or perhaps you need to create documentation that describes your system to the people who will be operating and/or maintaining/evolving it over time. If you cannot identify why and for whom you are creating a model then why are you bothering to work on it all? Your first step is to identify a valid purpose for creating a model and the audience for that model, then based on that purpose and audience develop it to the point where it is both sufficiently accurate and sufficiently detailed. Once a model has fulfilled its goals you're finished with it for now and should move on to something else, such as writing some code to show that the model works. This principle also applies to a change to an existing model: if you are making a change, perhaps applying a known pattern, then you should have a valid reason to make that change (perhaps to support a new requirement or to refactor your work to something cleaner). An important implication of this principle is that you need to know your audience, even when that audience is yourself. For example, if you are creating a model for maintenance developers, what do they really need ? Do they need a 500 page comprehensive document or would a 10 page overview of how everything works be sufficient ? Don't know ? Go talk to them and find out.
  • Plusieurs modèles : Vous avez potentiellement besoin d'utiliser plusieurs modèles pour développer votre logiciel parce que chacun de ces modèles décrira un aspect donné de votre logiciel. “Quels modèles sont potentiellement nécessaire pour build modern-day business applications?” Considering the complexity of modern day software, you need to have a wide range of techniques in your intellectual modeling toolkit to be effective. An important point is that you don't need to develop all of these models for any given system, but that depending on the exact nature of the software you are developing you will require at least a subset of the models. Different systems, different subsets. Just like every fixit job at home doesn't require you to use every tool available to you in your toolbox, over time the variety of jobs you perform will require you to use each tool at some point. Just like you use some tools more than others, you will use some types of models more than others.
  • Travail de qualité : Personne n'aime le travail bâclé. Ceux qui le font ne l'aiment pas parce que ce n'est pas quelque chose dont ils peuvent être fiers, et ceux qui viennent plus tard pour le refactorer (pour une raison ou une autre) ne l'aiment pas parce que c'est plus difficile à comprendre et à modifier, et les utilisateurs finaux n'aimeront pas le travail parce qu'il sera probablement instable et ne correspondra pas à leurs attentes.
  • Retour rapide : Le temps entre une action et le retour sur cette action est critique. En travaillant avec d'autres personnes sur un modèle, particularly when you are working with a shared modeling technology (such as a whiteboard, CRC cards, or essential modeling materials such as sticky notes) you are obtaining near-instant feedback on your ideas. Working closely with your customer, to understand the requirements, to analyze those requirements, or to develop a user interface that meets their needs, provides opportunities for rapid feedback.
  • Le logiciel comme but premier. L'objectif du développement logiciel est de produire un logiciel qui répond efficacement aux besoins de la MOA. Le but premier n'est pas de produire une documentation extérieurs, des artefacts de gestion de projet extérieurs, ou même des modèles. Toute activité qui ne contribue pas directement à ce but premier doit être mise en question et évitée si elle ne peut être justifiée à cette occasion.
  • Travel Light. Every artifact that you create, and then decide to keep, will need to be maintained over time. If you decide to keep seven models, then whenever a change occurs (a new/updated requirement, a new approach is taken by your team, a new technology is adopted, ...) you will need to consider the impact of that change on all seven models and then act accordingly. If you decide to keep only three models then you clearly have less work to perform to support the same change, making you more agile because you are traveling lighter. Similarly, the more complex/detailed your models are, the more likely it is that any given change will be harder to accomplish (the individual model is "heavier" and is therefore more of a burden to maintain). Every time you decide to keep a model you trade-off agility for the convenience of having that information available to your team in an abstract manner (hence potentially enhancing communication within your team as well as with project stakeholders). Never underestimate the seriousness of this trade-off. Someone trekking across the desert will benefit from a map, a hat, good boots, and a canteen of water they likely won't make it if they burden themselves with hundreds of gallons of water, a pack full of every piece of survival gear imaginable, and a collection of books about the desert. Similarly, a development team that decides to develop and maintain a detailed requirements document, a detailed collection of analysis models, a detailed collection of architectural models, and a detailed collection of design models will quickly discover they are spending the majority of their time updating documents instead of writing source code.
  • (optionnel) Le contenu est plus important que la représentation. Any given model could have several ways to represent it. For example, a UI specification could be created using Post-It notes on a large sheet of paper (an essential or low-fidelity prototype), as a sketch on paper or a whiteboard, as a "traditional" prototype built using a prototyping tool or programming language, or as a formal document including both a visual representation as well as a textual description of the UI. An interesting implication is that a model does not need to be a document. Even a complex set of diagrams created using a CASE tool may not become part of a document, instead they are used as inputs into other artifacts, very likely source code, but never formalized as official documentation. The point is that you take advantage of the benefits of modeling without incurring the costs of creating and maintaining documentation.
  • (optionnel) Chacun peut apprendre de l'autre : You can never truly master something, there is always opportunity to learn more and to extend your knowledge. Take the opportunity to work with and learn from others, to try new ways of doing things, to reflect on what seems to work and what doesn't. Technologies change rapidly, existing technologies such as Java evolve at a blinding pace and new technologies such as C# and .NET are introduced regularly. Existing development techniques evolve at a slower pace but they still evolve -- As an industry we've understood the fundamentals of testing for quite awhile although we are constantly improving our understanding through research and practice. The point to be made is that we work in an industry where change is the norm, where you must take every opportunity to learn new ways of doing things through training, education, mentoring, reading, and working with each other.
  • (optionnel) Connaissez vos modèles : Because you have multiple models that you can apply you need to know their strengths and weaknesses to be effective in their use.
  • (optionnel) Connaissez vos outils : Software, such as diagramming tools or modeling tools, have a variety of features. If you are going to use a modeling tool then you should understand its features, knowing when and when not to use them.
  • Local Adaptation. Your approach to software development must reflect your environment, including the nature of your organization, the nature of your project stakeholders, and the nature of your project itself. Issues that could be affected include: the modeling techniques that you apply (perhaps your users insist on concrete user interfaces instead of initial sketches or essential prototypes); the tools that you use (perhaps there isn't a budget for a digital camera, or you already have licenses for an existing CASE tool); and the software process that you follow (your organization insists on XP, or RUP, or their own process). You will adapt your approach at both the project level as well as the individual level. For example, some developers use one set of tools over another, some focus on coding with very little modeling whereas others prefer to invest a little more time modeling.
  • (optionnel) Communication ouverte et honnête : People need to be free, and to perceive that they are free, to offer suggestions. This includes ideas pertaining to one or more models, perhaps someone has a new way to approach a portion of the design or has a new insight regarding a requirement; the delivery of bad news such as being behind schedule; or simply the current status of their work. Open and honest communication enables people to make better decisions because the quality of the information that they are basing them on is more accurate.
  • (optionnel) Travailler avec l'instinct des gens : When someone feels that something isn't going to work, that a few things are inconsistent with one another, or that something doesn't "smell right" then there is a good chance that that is actually the case. As you gain experience developing software your instincts become sharper, and what your instincts are telling you subconsciously can often be an important input into your modeling efforts. If your instincts tell you that a requirement doesn't make sense or it isn't complete investigate it with your users. If your instincts tell you that a portion of your architecture isn't going to meet your needs build a quick technical end-to-end prototype to test out your theory. If your instincts tell you that design alternative A is better than design alternative B, and there is no compelling reason to choose either one of them, then go with alternative A for now. It's important to understand that the value of courage tells you that should assume you can remedy the situation at some point in the future if you discover your instincts were wrong.
• Pratiques :
  • Participation active des parties : An expansion of XP's On-Site Customer which describes the need to have on-site access to users that have the authority and ability to provide information pertaining to the system being built and to make pertinent and timely decisions regarding the requirements, and prioritization thereof. AM expands XP's On-Site Customer practice to have project stakeholders -- including direct users, their management, senior management, operations staff, and support (help desk) staff -- actively involved in the project. This includes making timely resourcing decisions by senior management, public and private support for the project by senior management, active participation of operations and support staff in the development of requirements and models pertaining to their respective areas.
  • Appliquer les bons artefacts : Each artifact has its own specific applications. For example, a UML activity diagram is useful for describing a business process, whereas the static structure of your database is better represented by a physical data or persistence model. Very often a diagram is a better choice than source code -- If a picture is worth a thousand words then a model is often worth 1024 lines of code when applied in the right circumstances (a term borrowed from Karl Wieger’s Software Requirements) because you can often explore design alternatives more effectively by drawing a couple diagrams on whiteboards with your peers than you can by sitting down and developing code samples. The implication is that you need to know the strengths and weaknesses of each type of artifact so you know when and when not to use them. Note that this can be very difficult because you have Multiple Models available to you, in fact the essay Artifacts For Agile Modeling: The UML and Beyond lists over 30 types of models and it is by no means definitive.
  • Propriété collective : Everyone can work on any model, and in fact any artifact on the project, if they need to.
  • Considérer la testabilité : When you are modeling you should be constantly asking yourself "How are we going to test this?" because if you can't test the software that you are building you shouldn't be building it. Modern software processes include testing and quality assurance activities throughout the entire project lifecycle, and some even promote the concept of writing tests first before writing software (this is an XP practice).
  • Créer plusieurs modèles en parallèle : Parce que chaque type de modèle a ses forces et faiblesses, un seul modèle ne suffit pas à vos besoins de modélisation. Par exemple lorsque vous explorez les besoins vous pouvez avoir besoin de développer des cas d'utilisation ou user stories, un prototype d'IHM, des règles métiers essentiels. In combination with the practice of iterating to another artifact les modéliseurs agiles découvriront souvent qu'ils sont bien plus productifs lorsqu'ils travaillent sur divers modèles en même temps que s'ils se concentraient sur un seul à chaque fois.
  • Créer un contenu simple : You should keep the actual content of your models -- your requirements, your analysis, your architecture, or your design -- as simple as you possibly can while still fulfilling the needs of your project stakeholders. The implication is that you should not add additional aspects to your models unless they are justifiable -- if you do not have a requirement to add system auditing features then don't add that features to your models. Have the courage to trust that you can in fact add this feature when, and if, it is ever asked of you. This is along the lines of XP's practice of Simple Design.
  • Dépeindre les modèles simplement : When you consider the potential diagrams that you could apply (UML diagrams, user interface diagrams, data models, and so on) you quickly realize that the majority of the time you only require a subset of the diagramming notation available to you. A simple model that shows the key features that you are trying to understand, perhaps a class model depicting the primary responsibilities of classes and the relationships between them, often proves to be sufficient. Yes, you could model all the scaffolding code that you will need to write, all the getter and setter operations that your coding standards tell you to use, but what value would that add? Very little.
  • Affichez vos modèles à la vue de tous. Vous devriez montrer vos modèles publiquement, souvent sur ce que l'on appelle un "mur de modélisation" ou "mur des merveilles". Cela soutient le principe de Communication Ouverte et Honnête dans votre équipe parce que l'ensemble des modèles en cours leur sont rapidement accessibles, ainsi qu'à votre MOA parce que vous ne leur cachez rien. Your modeling wall is where you post your models for everyone to see; the modeling wall should be accessible to your development team and other project stakeholders. Your modeling wall may be physical, perhaps a designated whiteboard for your architecture diagram(s) or a place where you tape a printout of your physical data model. Modeling walls can be virtual, such as an internal Web page that is updated with scanned images. See Ellen Gottesdiener's Specifying Requirements With a Wall of Wonder for a similar viewpoint.
  • Itérez sur un autre artefact. Lorsque vous travaillez sur un artefact de développement -- comme un cas d'utilisation, une carte CRC, un diagramme de séquence ou même du code source -- and find that you are stuck then you should consider working on another artifact for the time being. Each artifact has its strengths and weaknesses, each artifact is good for a certain type of job. Whenever you find you are having difficulties working on one artifact, perhaps you are working on a use case and find that you are struggling to describe the business logic, then that's a sign that you should iterate to another artifact. For example, if you are working on an essential use case then you may want to consider changing focus to start working on an essential UI prototype, a CRC model, a business rule, a system use case, or a change case. By iterating to another artifact you immediately become "unstuck" because you are making progress working on that other artifact. Furthermore, by changing your point of view you often discover that you address whatever it was that causing you to be stuck in the first place.
  • Modéliser par petits incréments : Le développement incrémental qui organise un vaste effort en plus petites portions diffusées au fil du projet, normalement en incréments de quelques semaines ou d'un mois ou deux, accroit votre agilité en permettant de mettre plus vite le logiciel dans les mains des utilisateurs.
  • Modéliser avec les autres : When you Model With a Purpose you often find that you are modeling to understand something, that you are modeling to communicate your ideas to others, or you are seeking to develop a common vision on your project. This is a group activity, one in which you want the input of several people working together effectively. You will often find that your development team needs to work together to create the core set of models critical to your project. For example, to develop the metaphor or architecture for you system, you will often need to model with a group of people to develop a solution everyone agrees on as well as one that is as simple as possible. Most of the time the best way to do this is to talk the issue through with one or more people.
  • Prouver par le code : A model is an abstraction, one that should accurately reflect an aspect of whatever you are building. But will it work? To determine so, you should prove your model with code. You've developed a sketch of an HTML page for accepting billing address information? Code it and show the resulting user interface to your users for feedback. You've developed a UML sequence diagram representing the logic to implement a complex business rule? Write the testing code, the business code, and run the tests to ensure that you've gotten it right. Never forget that with an iterative approach to software development, the norm for the vast majority of projects, that modeling is only one of many tasks that you will perform. Do some modeling, do some coding, do some testing (amongst other things).
  • Utiliser les outils les plus simples : The vast majority of models can be drawn on a whiteboard, on paper or even the back of a napkin. Whenever you want to save one of these diagrams you can take a picture of it with a digital camera, or even simply transcribe it onto paper. This works because most diagrams are throwaways; their true value comes from drawing them to think through an issue, and once the issue is resolved the diagram doesn’t offer much value. As a result a whiteboard and markers are often your best modeling tool alternative: Use a drawing tool to create diagrams to present to important project stakeholders and occasionally use a modeling tool if and only if they provide value to my programming efforts such as the generation of code. Think of it like this: If you’re creating simple models, often models that are throwaways because if you are modeling to understand you likely don’t need to keep the model(s) around any more once you do understand the issue, then you likely don’t need to apply a complex modeling tool.
  • (optionnel) Apply Modeling Standards : This practice is renamed from XP's Coding Standards, the basic idea is that developers should agree to and follow a common set of modeling standards on a software project. Just like there is value in following common coding conventions, clean code that follows your chosen coding guidelines is easier to understand and evolve than code that doesn't, there is similar value in following common modeling conventions. There is a wide variety of common modeling standards available to you, including the Object Management Group's Unified Modeling Language (UML) which defines the notation and semantics for common object-oriented models. The UML provides a good start but it isn't sufficient -- as you can see in Be Realistic About The UML not all possible modeling artifacts are encompassed by the UML. Furthermore, it says nothing about modeling style guidelines to create clean-looking diagrams. What is the difference between a style guideline and a standards. WRT to source code, a standard would be to name attributes in the format attributeName whereas a style guideline is to indent the code within a control structure (an if statement, a loop, ...) by one unit. WRT to models, a standard would be to use a square rectangle to model a class on a class diagram and a style guideline would be to have subclasses placed on diagrams to the south of their superclasses.
  • (optionnel) Apply Patterns Gently : Effective modelers learn and then appropriately apply common architectural, design and analysis patterns in their models. However, as Martin Fowler points out in Is Design Dead? developers should consider easing into the application of a pattern, to apply it gently. This reflects the value of simplicity. In other words, if you SUSPECT that a pattern applies you should model it in such a way as to implement the minimal amount you need today but that makes it easy to refactor it later when it is clear that applying the full-fledged pattern is in fact the simplest approach possible. In other words, don't over model. For example, you may recognize a good spot in your design to apply the GoF's Strategy pattern, but at the current moment you only have two algorithms to implement. The simplest approach might be to encapsulate each strategy in its own class and build an operation that chooses them appropriately and passes them the appropriate input. This is a partial implementation of Strategy that leaves you in a position to refactor your design if more algorithms need to be implemented, yet does not require you to build all the scaffolding that Strategy requires -- an approach that enables you to ease into application of the pattern.
  • (optionnel) Supprimer les modèles temporaires : The vast majority of the models that you create are temporary/working models -- design sketches, low fidelity prototypes, index cards, potential architecture/design alternatives, and so on -- models that have fulfilled their purpose but no longer add value now that they have done so. Models quickly become out of sync with the code, and there is nothing wrong with that. You must then make the decision to synchronize the models if doing so adds value to your project or to simply discard them because the investment to update the models won't be recouped by the value of having done so (there's negative payback).
  • (optionnel) Formaliser des modèles contractuels : Contract models are often required when an external group controls an information resource that your system requires, such as a database, legacy application or information service. A contract model is something that both parties should mutually agree to and mutually change over time if required. Examples of contract models include the detailed documentation of an application programming interface (API), a file layout description, an XML DTD or a physical data model describing a shared database. As with a legal contract, a contract model often requires you to invest significant resources to develop and maintain the contract to ensure that it’s accurate and sufficiently detailed. Your goal is to minimize the number of contract models for your system to conform to the XP principle of traveling light. Note that you will almost always use an electronic tool to develop a contract model because the model must be maintained over time.
  • (optionnel) Modéliser pour communiquer. A secondary reason to model is to communicate with people external to your team or to create a contract model. Because the customers for some models are outside your team, you may need to invest the time to make your model(s) look “pretty” by using electronic tools such as word processors, drawing packages or even sophisticated CASE tools.
  • (optionnel) Modéliser pour la compréhension : The most important application of modeling is to explore the problem space, to identify and analyze the requirements for the system, or to compare and contrast potential design alternatives to identify the potentially most simple solution that meets the requirements. Following this practice you often develop small, simple diagrams that focuses on one aspect of your software, such as the life cycle of a class or the flow between screens, diagrams that you often throwaway once you are finished with them.
    Reuse Existing Resources. There is a wealth of information that agile modelers can take advantage from. For example, perhaps some analysis or design patterns are appropriate for you to apply gently to your system. Or perhaps you can take advantage of an existing enterprise requirements model, business process models, physical data models or even models of how systems are currently deployed within your user community. It’s true that these models either don’t exist or are out of date in many organizations, although you’re often likely to uncover reasonably accurate models with a bit of research.
  • (optionnel) Mettre à jour seulement si cela pose problème : You should update a model only when you absolutely need to, when not having the model updated is more painful than the effort of updating it. With this approach you discover that you update a smaller number of models than you would have in the past because the reality is that your models don't have to be perfect to provide value. The street map that I have to my town is over five years old, I know this because my own street doesn't appear on it and it's been in place for a little over five years, yet the map is still useful to me. Yes, I could purchase an updated map, one comes out every year, but why bother? Missing a few streets isn't painful enough to warrant this investment, it simply doesn't make sense to spend the money to purchase a new map every year when the one that I have is good enough. Too much time and money is wasted trying to keep models and documents in sync with source code, an impossible task to begin with, time and money that could be better spent developing new software.
  • (complémentaire) Remaniement (refactoring). C'est une pratique de codage dans laquelle vous effectuez de petits changements, nommés remaniements, sur votre code pour répondre à de nouveaux besoins ou pour maintenir votre conception aussi simple que possible. Du point de vue AM cette pratique garanti que votre conception reste claire et nette lorsque vous travaillez sur votre code. Le remaniement est une partie essentielle de XP.
  • (complémentaire) Conception par tests préliminaires : C'est une pratique de développement où vous considérez en premier puis codez vos cas de tests avant d'écrire votre code métier. Du point de vue AM cette pratique vous force à concevoir avant d'écrire votre code, éliminant le besoin d'une modélisation détaillée. La conception par tests préliminaires est une partie essentielle de XP.

Caractéristiques

• Parfois appelés "processus légers"
• Réputés adapté aux petits projets seulements, ce que les défenseurs de l'Agile Manifesto contestent ;
• La force des modèles AM est de ne pas chercher à être parfaits, mais juste corrects. AM peut s'appliquer indifféremment à l'étude des besoins, l'architecture, conception.

Limitations

• Preuves à faire sur de grands projets.

Exemples

Des exemples de méthodes agiles sont :

• Crystal
• ASD
• XBreed (Scrum + XP)
  • Scrum
  • XP
• FDD
• DSDM
• PP

Voir

• Agile Alliance
• Agile Modeling (AM) Home Page
• Business Process Partners - Méthodes