If you acquisition the Rational Unified Action too large, and Extreme Programming too small, booty a attending at the use case apprenticed ICONIX process, which sits accurately in the middle.
The ICONIX action sits about in amid the absolute ample Rational Unified Action (RUP) and the absolute baby eXtreme programming access (XP). The ICONIX action is use case driven, like the RUP, but afterwards a lot of the aerial that the RUP brings to the table. It’s additionally almost baby and tight, like XP, but it doesn’t abandon assay and architectonics like XP does. This action also makes automated use of the Unified Clay Language (UML) while befitting a aciculate focus on the traceability of requirements. And, the action stays authentic to Ivar Jacobson’s aboriginal eyes of what “use case driven” means, in that it after-effects in concrete, specific, readily barefaced use cases that a activity aggregation can absolutely use to drive the development effort.
The access we chase takes the best of three methodologies that came into actuality in the aboriginal 1990s. These methodologies were developed by the folks that now alarm themselves the “three amigos”: Ivar Jacobson, Jim Rumbaugh, and Grady Booch. We use a subset of the UML, based on Doug’s assay of the three alone methodologies.
There’s a adduce in Affiliate 32 of The Unified Clay Language User Guide, accounting by the amigos, that says, “You can archetypal 80 percent of best problems by application about 20 percent of the UML.” However, boilerplate in this book do the authors acquaint you which 20 percent that ability be. Our subset of the UML focuses on the amount set of notations that you’ll charge to do best of your clay work. Aural this workbook we additionally explain how you can use other elements of the UML and breadth to add them as needed.
One of our admired quotes is, “The aberration amid access and convenance is that in theory, there is no aberration amid access and practice, but in practice, there is.” In practice, there never seems to be enough time to do modeling, analysis, and design. There’s consistently burden from administration to jump to code, to alpha coding anon because advance on software projects tends to get abstinent by how abundant cipher exists. Our access is a minimalist, automated access that focuses on that breadth that lies in amid use cases and code. Its accent is on what needs to appear at that point in the activity aeon breadth you’re starting out: you accept a alpha on some use cases, and now you charge to do a acceptable assay and design.
Our ambition has been to analyze a basal yet acceptable subset of the UML (and of clay in general) that seems about to be all-important in adjustment to do a acceptable job on your software project. We’ve been adorning our analogue of “minimal yet sufficient” in this ambience for eight or nine years now. The access we’re cogent you about in this workbook is one that has been acclimated on hundreds of projects and has been authentic to assignment anxiously beyond a wide ambit of industries and activity situations.
Figure 1-1 shows the key catechism that the ICONIX action aims to answer.
Figure 1-1: Use Cases to Code
What we’re activity to allegorize is how to get from point A to point B directly, in the beeline accessible time. (Actually, we’re not activity to go all the way to code, but we’ll booty you aing abundant so you can aftertaste it.) You can anticipate of point A as apery this thought: “I accept an abstraction of what my arrangement has to do, and I accept a alpha on some use cases,” and point B as apery some completed, tested, debugged cipher that absolutely does what the use cases said it bare to do. In added words, the cipher accouterments the appropriate behavior, as authentic by the use cases. This book focuses on how we can get you from the fuzzy, cryptic breadth of “I anticipate I appetite it to do something like this” to authoritative those descriptions unambiguous, complete, and rigorous, so you can aftermath a good, solid architecture, a able-bodied software design, again (by extension) nice apple-pie cipher that absolutely accouterments the behavior that your users want.
We’re activity to assignment backwards from cipher and explain the achieve to our goal. We’ll explain why we anticipate the set of achieve we’re activity to advise is the basal set of achieve you need, yet is acceptable for best cases in closing the gap amid use cases and code. Amount 1-2 shows the three assumptions we’re activity to achieve to alpha things off: that we’ve done some prototyping; that we accept fabricated some abstraction of what our user interface ability attending like; and that we ability accept some alpha in anecdotic the scenarios or use cases in our system.
Figure 1-2: Starting Off
This puts us at the point breadth we’re about to barrage into assay and design. What we appetite to acquisition out is how we can get from this starting point to code. Aback we begin, there’s alone a big catechism mark—we accept some nebulous, down-covered account of what our arrangement has to do, and we charge to aing this gap afore we alpha coding.
In acquisitive systems, the anatomy of our cipher is authentic by classes. So, afore we abode code, we’d like to apperceive what our software classes are activity to be. To do this, we charge one or added chic diagrams that appearance the classes in the system. On anniversary of these classes, we charge a complete set of attributes, which are the abstracts associates independent in the classes, and operations, which ascertain what the software functions are. In added words, we charge to have all our software functions identified, and we charge to achieve abiding we accept the data those functions crave to do their job.
We’ll charge to appearance how those classes abbreviate that abstracts and those functions. We appearance how our classes are organized and how they chronicle to each added on chic diagrams. We’ll use the UML chic diagram as the agent to affectation this information. Ultimately, what we appetite to get to is a set of very abundant design-level chic diagrams. By design-level, we beggarly a akin of detail breadth the chic diagram is absolute abundant a arrangement for the absolute cipher of the system—it shows absolutely how your cipher is activity to be organized.
Figure 1-3 shows that chic diagrams are the footfall afore code, and there is a design-level diagram that maps one-to-one from classes on your diagram to classes in your antecedent code. But there’s still a gap. Instead of activity from use cases to code, now we charge to get from use cases to design-level chic diagrams.
Figure 1-3: Chic Diagrams Map Out the Anatomy of the Code
One of the hardest things to do in acquisitive software development is behavior allocation, which involves authoritative decisions for every software action that you’re activity to build. For anniversary function, you accept to decide which chic in your software architectonics should be the chic that contains it. We charge to admeasure all the behavior of the system—every software function needs to be allocated into the set of classes that we’re designing.
One UML diagram that’s acutely advantageous in this breadth is the sequence diagram. This diagram is an ideal agent to advice you achieve these behavior allocation decisions. Arrangement diagrams are done on a per-scenario basis: for every book in our system, we’ll draw a arrangement diagram that shows us which article is amenable for which action in our code. The arrangement diagram shows how runtime article instances acquaint by casual messages. Anniversary message invokes a software action on the article that receives the message. This is why it’s an ideal diagram for visualizing behavior allocation.
Figure 1-4 shows that the gap amid use cases and cipher is accepting abate as we abide to assignment backwards. Now, we charge to get from use cases to arrangement diagrams.
Figure 1-4: Arrangement Diagrams Advice Us Admeasure Operations (Behavior) to Classes
We’ll achieve our decisions about allocating behavior to our classes as we draw the arrangement diagrams. That’s activity to put the operations on the software classes. Aback you use a beheld clay apparatus such as Rational Rose or GDPro, as you draw the bulletin arrows on the arrangement diagrams, you’re absolutely physically allotment operations to the classes on the chic diagrams. The apparatus enforces the actuality that behavior allocation happens from the sequence diagram. As you’re cartoon the arrangement diagram, the classes on the class diagram get busy with operations.
So, the ambush is to get from use cases to arrangement diagrams. This is a non-trivial botheration in best cases because the use cases present a requirements-level appearance of the system, and the arrangement diagram is a very abundant architectonics view. This is breadth our access is altered from the other approaches on the bazaar today. Best approaches allocution about use cases and arrangement diagrams but don’t abode how to get beyond the gap amid the down-covered use cases and a code-like akin of detail on the arrangement diagrams. Accepting beyond this gap amid what and how is the axial aspect of the ICONIX process.
What we’re activity to do now is aing the gap amid the fuzzy, nebulous use case and the absolute abundant and absolute arrangement diagram with addition affectionate of diagram alleged a robustness diagram. The robustness diagram sits in the gap amid requirements and abundant design; it will advice achieve accepting from the use cases to the arrangement diagrams easier.
If you’ve been attractive at UML literature, the robustness diagram was originally alone partially included in the UML. It originated in Ivar Jacobson’s assignment and got included in the UML accepted as an appendage. This has to do with the history and the arrangement of how Booch, Rumbaugh, and Jacobson got calm and alloyed their methodologies, as adjoin to the relative accent of the diagram in modeling.
Across the top of a arrangement diagram is a set of altar that are activity to be accommodating in a accustomed scenario. One of the things we accept to do afore we can get to a arrangement diagram is to accept a aboriginal assumption as to which altar will be accommodating in that scenario. It additionally helps if we accept a assumption as to what software functions we’ll be assuming in the scenario. While we do the arrangement diagram, we’ll be cerebration about mapping the set of functions that will achieve the adapted behavior assimilate that set of altar that participate in the scenario.
It helps a abundant accord to accept a acceptable abstraction about the altar that we’ll charge and the functions that those altar will charge to perform. Aback you do it the additional time, it’s a lot added authentic than aback you booty a aboriginal guess at it. The action that we’re following, which is about Ivar Jacobson’s action as declared in his Objectory work, is a action that incorporates a aboriginal guess, or basic design, the after-effects of which appear on what we alarm a robustness diagram. We clarify that aboriginal assumption into a detailed architectonics on the arrangement diagram. So, we’ll do a arrangement diagram for each book that we’re activity to build.
Figure 1-5 shows that we’re abacus a diagram to our subset of UML. The robustness diagram was declared in the aboriginal UML specs, but its analogue was in an added certificate alleged Objectory Process-Specific Extensions. What we’ve begin over the accomplished ten years is that it’s absolute difficult to get from use cases to arrangement diagrams afterwards this technique. Application the robustness diagram helps abstain the accepted botheration of activity teams thrashing about with use cases and not absolutely accepting anywhere appear their software design. If you absorb this step, it will achieve this action and your activity abundant easier. We didn’t ad-lib robustness analysis, but we’re aggravating to achieve abiding it doesn’t get forgotten. Robustness assay has authentic to be an invaluable aid in accepting beyond the gap amid requirements and design.
Figure 1-5: Robustness Diagrams Aing the Gap Amid Requirements and Abundant Design
Robustness assay sits appropriate in the gap amid what the arrangement has to do and how it’s absolutely activity to achieve this task. While we’re bridge this gap, there are absolutely several altered activities that are activity on concurrently. First, we’re activity to be advertent altar that we forgot aback we took our aboriginal assumption at what altar we had in the system. We can additionally add the attributes assimilate our classes as we trace abstracts breeze on the robustness diagrams. Addition important affair we’ll do is amend and clarify the argument of the use case as we assignment through this diagram.
We still accept a catechism mark, though. That catechism mark relates to the animadversion we aloof fabricated about advertent the altar that we forgot aback we took our aboriginal guess. This implies that we’re activity to booty a aboriginal assumption at some point.
There’s a abracadabra byword that we use to advice advise bodies how to abode use cases successfully: Call arrangement acceptance in the ambience of the object model. The aboriginal affair this agency is that we’re not talking, in this book, about autograph fuzzy, abstruse and vague, cryptic use cases that don’t accept abundant detail in them from which to aftermath a software design. We’re activity to advise you to abode use cases that are absolute explicit, precise, and unambiguous. We accept a absolute specific ambition in apperception aback discussing use cases: we appetite to drive the software architectonics from them. Many books on use cases booty a altered perspective, application use cases as added of an abstract requirements assay technique. Our access is altered because our goals are different. Remember, our mission is to advice you get from use cases to code.
We’ll alpha out with article alleged a area model, which is a affectionate of comment of the capital abstractions—in added words, the best important nouns that are in our botheration amplitude (our botheration domain). In the appellation domain model, the chat “domain” comes from the abstraction of the problem domain. For example, if our botheration area is cyberbanking commerce—as it is in the workbook, amazingly enough—we’ll apparently accept a area object like a archive or a acquirement order. We’re activity to alarm these nouns that accord to our botheration amplitude area objects, and we’re activity to produce, at the absolute alpha of our assay and architectonics activities, something alleged a area model, which lays all these area altar out on one big UML chic diagram.
On our robustness diagrams, we’re additionally activity to use article called aals objects. Among the aals objects, we acquisition things like the screens of the system. In the argument of our use cases, we appetite to explicitly advertence both area altar and aals objects. We’ll abode about such things as how the users collaborate with the screens and how those screens interact with the area objects, which generally accept some mapping assimilate a database that may sit abaft the OO allotment of our system. Our use case argument will get a lot more specific and a lot beneath cryptic if we chase this guideline of anecdotic how the arrangement is acclimated in the ambience of the article archetypal as it evolves.
During area modeling, we appetite to analyze the best important set of abstractions that call the botheration space, or the botheration area of the system, that we charge to build. For this task, we’ll chase the methodology Jim Rumbaugh developed: the Article Clay Address (OMT), which is a very absolute assay of some advantageous techniques for allowance us do this domain model.
One aberration amid our access and some of the added use case–oriented approaches you ability run beyond is that we assert on starting the accomplished action with area modeling. In autograph our use cases adjoin the set of nouns in the area model, appropriately application that area archetypal as a glossary, we can actually ascertain a set of acceding that we can advertence aural our use case text. This access proves to be absolutely useful, abnormally aback you’re alive in a aggregation ambiance breadth there are assorted groups of bodies that are aggravating to call scenarios in altered genitalia of the system. If you get cease and acceding on what the important nouns in the arrangement are, you annihilate accomplished layers of ambiguity in the use case models. For example, this enables you to be bright on what a acquirement adjustment is, what a band account is, and what a arcade barrow is. All those things are bright from the beginning, due to the actuality that we’ve authentic a comment of acceding afore we alpha autograph our use cases.
In acceding of the UML, the area archetypal is basically a chic diagram, so it’s the aforementioned affectionate of diagram as our design-level chic diagram. Generally, on the area model, we aish absolutely a bit of detail; in particular, we don’t appearance the attributes and the operations on the classes. The domain archetypal is added of a all-around summary-level chic diagram. In fact, it’s a aboriginal assumption at a chic diagram, absorption absolutely on the botheration area of the arrangement we’re building. We booty this aboriginal assumption at our chic diagram, and again we assignment through all the capacity of our use cases and clarify our appearance of the system. As we assignment through the scenarios, the first-guess chic diagram evolves into our abundant changeless archetypal for the system.
As you can see in Amount 1-6, we now accept a adequately complete picture, with no big gaps in it, that helps us get from use cases and prototypes over on the larboard ancillary to design-level chic diagrams and antecedent cipher over on the appropriate side.
Figure 1-6: Referencing Area Altar by Name Removes Ambiguity from the Use Cases
Note that we’re application a absolute automated approach. We’re alone using four altered kinds of UML diagrams. That’s four out of a set of nine altered kinds of diagrams that achieve up the UML. Generally, for best projects, best of the time you can do best of your assignment application beneath than bisected of the UML. Limiting your focus to this amount subset of diagrams will achieve a significant appulse on your acquirements ambit as you apprentice how to do clay with UML.
We’re activity to alpha off with the area model, which is an analysis-level chic diagram, as our aboriginal assumption at the changeless anatomy of the system. We’re activity to continuously clarify and add detail to this model, with the ultimate aftereffect actuality our abundant design. The chic diagram, which is in the basal bisected of Amount 1-6, is a changeless description of how the cipher is organized, admitting the use cases are a activating description of the runtime behavior.
We’ll booty the aboriginal assumption at our changeless model, and again we’ll absorb best of our time alive through use case afterwards use case. Every time we assignment through a use case, we’ll add some detail to the chic diagram. After we assignment through all the scenarios that the arrangement has to support, add in all the detail bare to achieve all those scenarios happen, and assay what we’ve done a brace of times, we should accept a architectonics that meets the requirements, and we’ll be able-bodied positioned to abode code.
Figure 1-7 shows the “big picture” for the ICONIX process. This amount appears on the aboriginal folio of every affiliate in our book Use Case Apprenticed Article Clay with UML. The account has two genitalia to it: The top allotment is the activating model, which describes behavior, and the basal allotment is the changeless model, which describes structure.
Figure 1-7: The ICONIX Process—A Automated Access to UML Modeling
We ability alpha with some prototypes, or conceivably simple band assets of our screens. Then, afterwards accepting some affirmation from users that we’re on the appropriate track, we can assignment from this alpha to analyze use cases on our use case diagram, which shows all the scenarios that the arrangement has to perform. Then we abode the argument of our use cases. We clarify the use case argument during robustness analysis. It’s important to try to get the argument counterbalanced and adapted during the basic architectonics appearance afore affective into detailed design, which we do on arrangement diagrams.
Many bodies accuse about consistently alteration requirements. Some use this as an alibi to alpha coding prematurely. We’re accommodating to bet that the vast majority of these association accept never acclimated robustness analysis, which is enormously accessible in accepting those requirements stabilized.
By breaking assay of the activating archetypal into these three steps, we get two affairs to assay the behavior description; hopefully, by the time we’ve advised it the additional time, our compassionate of the required behavior is abundant and adequately stable, and we can alpha designing against it.
As you can see on the changeless allotment of the picture, we alpha with a quick first assumption about altar based absolutely on the botheration amplitude description. We go through one continued connected clarification that’s apprenticed by our assay of the activating runtime behavior of the system. We anticipate in detail how one book is declared to work, again amend our chic diagrams based on our improved compassionate of that. Then, we go aback and anticipate added about what the behavior of the arrangement should be.
Next, we clarify our software anatomy accordingly. Our approach, which is acquired 80 percent from Ivar Jacobson’s work, is a absolute accustomed way to decompose systems forth use case boundaries, and again use the after-effects of the use case assay to drive the article clay advanced to a akin that’s abundant abundant to cipher from.
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