The Essentials of Modern Software Engineering. Ivar Jacobson
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We will develop these concepts throughout the book, but for now focus in a bit more on each of these differentiated Things to Work With.
5.2.1 Alphas
Alphas, again, are aspects of a software endeavor whose evolution we want to understand, monitor, direct, and control. Why are they called alphas? The developers of Essence, in searching for a word to describe these important key elements, chose the word alpha, which has been used to denote important elements such as a position in a social hierarchy or the first (often the brightest) star in a constellation (examples from Wikipedia). The alphas bound the work to be accomplished in progressing toward the provisioning of the software system. Alphas are portrayed as an icon that is a stylized variant of the first letter of the Greek alphabet (see Figure 5.1 and Table 5.1).
Simply put, alphas are the most important things you must attend to and progress in order to be successful in a development endeavor.
Although an alpha is commonly understood or evidenced by one or more associated work products (which thus describe particular aspects of it), it is not tangible by itself, so there must at least be tacit knowledge linked to each alpha. One form of this knowledge is the alpha’s state.
5.2.2 Alpha States
Alphas have states that describe progression through a lifecycle. As an example, Essence defines the states of the Requirements alpha as follows.
Conceived. The need for a new system has been agreed upon.
Bounded. The purpose and theme of the new system are clear.
Figure 5.2 Requirements alpha card.
Coherent. The requirements provide a consistent description of the essential characteristics of the new system.
Acceptable. The requirements describe a system that is acceptable to the stakeholders.
Addressed. Enough of the requirements have been addressed to satisfy the need for a new system in a way that is acceptable to the stakeholders.
Fulfilled. The requirements have been addressed to fully satisfy the need for a new system.
To help remember the states of the Requirements alpha, Essence provides a poker card description, as shown in Figure 5.2. As we will discuss later, such poker-sized cards will also serve as teaching tools, and even make software engineering more fun through games.
Let’s consider the layout of the card. At the top left, you see the icon representing an alpha. This distinguishes it as an alpha card rather than a work product card, competency card, or any other element. The top of the card also highlights the name of the element—in this case, the Requirements—followed by a brief description of the alpha and the states of the alpha. (This is a very concise overview of the requirements alpha. For more details, refer to the Essence specification.)
Cards are also available for each alpha state, as shown in Figure 5.3, which shows six cards, one for each of the Requirements alpha states. The layout of each of these cards comprises the alpha icon and … by the standard. (These abbreviations make it possible to fit the checklists on the cards for easy, quick reference. If you do not find them to be fully understandable, you should refer to the full checklists in the Essence Quick Reference Guide, available for download from www.software-engineering-essentialized.com.)
Figure 5.3 Requirements alpha state cards.
The other alpha in our example, the Software System, has the states shown in Figure 5.4.
The states are defined on the basis of an incremental risk-driven approach to building the Software System, first by establishing a sound architecture, and then by demonstrating key decisions about the Software System. These states are summarized as follows.
Figure 5.4 Software System alpha card.
Architecture Selected. Key decisions about the Software System have been made. For instance, the most important system elements and their interfaces are agreed upon.
Demonstrable. Key use of the Software System has been demonstrated and agreed.
Usable. The Software System is usable from the point of view of its users.
Ready. The Software System has sufficient quality for deployment to production, and the production environment is ready.
Operational. The Software System is operating well in the production environment.
Retired. The Software System is retired and replaced by a new version of the Software System, or by a separate Software System.
5.2.3 Work Products
Work products, again, are tangible things such as documents and reports, and may provide evidence to verify the achievement of alpha states. An example of a work product for the Requirements alpha might be some kind of a requirements specification—a description of the software system to be built. When a complete and accepted requirements document has been developed, it can be one way to confirm having achieved certain checklists within a state of the Requirements alpha. Yet the fact that you have a document is not necessarily a sufficient condition to prove evidence of state achievement. Historically, documentation has not always provided an accurate measurement of progress. Thus, you may reach the same state without any documentation or with very brief documentation, as long as the checklist for that state has been achieved satisfactorily.
Figure 5.5 The Code work product card.
Code is the example of a work product for our programming practice. We provide a concise description of this work product in the form of a poker-sized card, as shown in Figure 5.5.
Note that the work products you produce do not belong to the common ground represented by the Essence standard. They are dependent on how you want to work (which practices you want to use). Thus, Essence does not specify exactly which work products are to be developed, but it does precisely specify what work products are, how you represent them, and what you can do with them.
Work products can have different levels of detail. In a development endeavor, the degree of detail needed in work products can vary greatly, depending on many factors such as past history of team members working together, customer requirements, regulatory requirements (e.g., regulation for software validation of medical devices), and organizational policies.
In TravelEssence, for example, Smith’s team expressed requirements through use case narratives, which we will cover in Part III. These also have different levels of detail. For simple requirements, Smith’s team did not need as many specifics, but relied on more direct communication with their stakeholders. However, for more sophisticated requirements involving complicated calculation and decision rules, Smith had more complete explanations in his use case narratives.