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<mainDescription>&lt;h3&gt; Use Case Formats &lt;/h3&gt;
&lt;p&gt; Use cases differ from project to project and person to person. A use case
that works in one situation may be totally unsuited for another. Different projects
have different needs. (See &lt;a class=&quot;elementLinkWithUserText&quot; href=&quot;./../../../openup_basic/guidances/supportingmaterials/references,_9ToeIB83Edqsvps02rpOOg.html&quot; guid=&quot;_9ToeIB83Edqsvps02rpOOg&quot;&gt;[ADO04]&lt;/a&gt;
for more information on use case formats.) &lt;/p&gt;
&lt;p&gt;Some need rigorous documentation, including &lt;strong&gt;high-ceremony use cases&lt;/strong&gt;,
which are formal, highly structured use cases. If the writers used a template,
then they filled out all or almost all of its fields for each use case. High-ceremony
use cases are best suited for large, extremely complex, safety-critical systems,
such as flight control systems, telephone switches, and so forth. They are also
used in development cultures that have high documentation standards. &lt;/p&gt;
&lt;p&gt;Other projects may be more agile and less formal, benefiting from &lt;strong&gt;low-ceremony
use cases&lt;/strong&gt;, which are informal, less rigidly structured use cases. If
the writers used a template, then they may have left many of the fields blank.
Low-ceremony use cases are best suited for smaller, less complex, less safety-critical
systems where most of the stakeholders have a strong background in the problem
domain. Sometimes, simple descriptions suffice, such as use case &lt;strong&gt;briefs&lt;/strong&gt;.
&lt;p&gt; As &lt;a class=&quot;elementLinkWithType&quot; href=&quot;./../../../openup_basic/guidances/guidelines/detail_ucs_and_scenarios,_4BJ_YCxSEdqjsdw1QLH_6Q.html&quot; guid=&quot;_4BJ_YCxSEdqjsdw1QLH_6Q&quot;&gt;Guideline:
Detail Use Cases and Scenarios&lt;/a&gt; explains, it makes sense to write use cases
iteratively. Starting with the basic details, you can then identify the various
alternative and error paths that the use case might follow so that you can evaluate,
rearrange, or eliminate them, and then elaborate or fill in the details of the
courses that you intended to use. You can then write the
use cases in&lt;strong&gt; &lt;/strong&gt; one or more of
the following formats, progressively, until you
reach the one with the level of detail required for a specific project: &lt;/p&gt;
&lt;li&gt;&lt;a id=&quot;Actor-Goal-List&quot; name=&quot;Actor-Goal_List&quot;&gt;&lt;strong&gt;Actor-Goal list&lt;/strong&gt;&lt;/a&gt;:
A format for the overview&lt;/li&gt;
&lt;li&gt; &lt;a id=&quot;Briefs&quot; name=&quot;Briefs&quot;&gt;&lt;strong&gt;Briefs: &lt;/strong&gt;&lt;/a&gt;A format for
writing summary use cases&lt;/li&gt;
&lt;li&gt; &lt;a id=&quot;Improvisational Score&quot; name=&quot;Improvisational Score&quot;&gt;&lt;strong&gt;Improvisational
score: &lt;/strong&gt;&lt;/a&gt;A format for writing less formal, low-ceremony use cases&lt;/li&gt;
&lt;li&gt; &lt;a id=&quot;Symphonic Score&quot; name=&quot;Symphonic Score&quot;&gt;&lt;strong&gt;Symphonic score:
&lt;/strong&gt;&lt;/a&gt;A format for writing more formal, high-ceremony use cases&lt;/li&gt;
&lt;h4&gt;Actor-Goal list &lt;/h4&gt;
&lt;p&gt; &lt;strong&gt;Context: &lt;/strong&gt;You have identified your actors and are trying to
identify use cases. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Problem:&lt;/strong&gt; Developing a set of use cases in an ad hoc manner
can lead to unnecessary work, missing features, and feature creep. Weight
is one of the most important factors in space flight &amp;#8212; so important that
the United States space agency, NASA, will not
allow anything on a spacecraft that isn’t absolutely critical to the flight.
If something literally isn’t worth its weight, then it doesn’t go. Likewise,
each use case adds cost to a system; therefore, you need to be sure to include
only those use cases that add some kind of value to your collection. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Forces:&lt;em&gt; &lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Simply listing actors or listing goals is not informative enough,
but actors and goals together are informative.&lt;/strong&gt; The classical approach
to writing use cases is to define a list of actors, then find use cases
for each. A variation on this theme is to itemize what the system must accomplish.
Yet, neither approach is adequate by itself. You need to know both who is
using the system and why they are using it. Otherwise, you introduce the
potential of either feature creep or missed features. At the least, a set
of use cases should describe this association. &lt;/p&gt;
&lt;p&gt;&lt;strong&gt; A quick overview of the entire project structure is sufficient
and necessary early in the use case development cycle.&lt;/strong&gt; Ideally,
this overview should be as short as reasonably possible. It must contain
key information as to who requires each service and why they need it. Most
other information is not very useful at this stage of the project, because
it runs the risk of quickly becoming obsolete, as well as discouraging
out-of-the-box (innovative) thinking. An overview
helps the writers work through the entire set from a high-level view, expanding
some use cases, eliminating others, and combining still others into a more
logical grouping. &lt;/p&gt;
&lt;p&gt;&lt;strong&gt;You need to be able to expand each to a full use case on demand.
&lt;/strong&gt;A &lt;em&gt;seedling&lt;/em&gt;&lt;strong&gt; &lt;/strong&gt;use case forms the basis for
a full use case later in the iterative development cycle. Each seedling
use case needs to convey enough information so that someone, possibly other
than the outline writer, can easily go back and expand it into a more informative
use case. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Solution: &lt;/strong&gt;Build an Actor-Goal list,
which is a list of actors and their goals that
gives you an overview of entire project needs.&lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;Start by identifying the list of actors who will use the system, and then
identify at least one goal for each. Actors without goals indicate that
you haven’t adequately defined the system. The actor is beyond the system’s
scope, doesn’t belong in the system, or is part of another actor. &lt;/p&gt;
&lt;p&gt;Likewise, leftover goals can indicate that the system is too complex and
you're trying to accomplish too much, or that you haven’t adequately defined
all of the necessary actors. Carefully evaluate the leftovers to see if
you are just overlooking some detail, or whether they don’t belong in the
system. &lt;/p&gt;
&lt;p&gt;Remove unassociated actors and goals from the list. &lt;/p&gt;
&lt;p&gt; Sometimes, this list may provide enough information to serve as use cases
for very small, high-communicating, low-ceremony project teams. Usually, the
actor goal list is the first step of identifying use cases. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Context: &lt;/strong&gt;You have written an Actor-Goal list that outlines
your use cases. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Problem: &lt;/strong&gt;Relying solely on an overview to capture the important
parts of a system’s behavior is dangerous, because it provides only high-level
information and can easily introduce ambiguity into a system. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Forces: &lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Although valuable, an Actor-Goal list does not clearly describe
a system.&lt;/strong&gt; Usually, an outline doesn’t provide enough precision
to avoid ambiguity, which can wreak havoc on a project by leading to unnecessary
or erroneous development. Yet, an outline is helpful, because you still
want an overview that you can easily scan. Unfortunately, with the passing
of time or sheer volume of work, it’s too easy to forget details
that were obvious to you earlier.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Iterative use case development requires creating placeholders for
expansion.&lt;/strong&gt; To develop use cases iteratively, you start with sparse
use cases, reorganize them, and flesh them out as the system takes shape.
Ideally, these placeholders should be clear enough to: 1) unambiguously
describe their role in the system, and 2) allow someone to expand the use
case, even if they were not involved in writing them originally. &lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Because outlines are general by nature, do not spend a lot of time,
energy, or money writing them. &lt;/strong&gt;Outlines provide an inexpensive
method of documenting complex ideas in a manner that is easy to follow,
and they provide a mechanism for people outside of a project to understand
the high-level concepts. While it may take
some effort to think things through, you don’t want to waste resources describing
your ideas. The system is still in a state of flux at this point, and it
is too early to spend much time documenting its shifting details. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Solution: &lt;/strong&gt;Write two to four sentences per use case, capturing
key activities and key-extension handling. &lt;/p&gt;
&lt;p&gt; Expand the Actor-Goal list into&lt;strong&gt; briefs&lt;/strong&gt; by writing a two-
to four-sentence use cases for each entry in the list. &lt;/p&gt;
&lt;p&gt;Briefly describe each use case’s main&amp;nbsp;scenario and most important
extensions. &lt;/p&gt;
&lt;p&gt; Include enough information to eliminate ambiguity for at least the main&amp;nbsp;scenario
of the system. &lt;/p&gt;
&lt;h4&gt; Improvisational score&lt;/h4&gt;
&lt;p&gt; &lt;strong&gt;Context: &lt;/strong&gt;You are operating in well-known domains or in situations
where writing high-ceremony use cases would require all of your allotted development
time. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Problem:&lt;/strong&gt; Writing formal, high-ceremony use cases when lesser
detail would suffice wastes time and resources. &lt;/p&gt;
&lt;p&gt; Jazz is considered to be “musician’s music,” and jazz players are usually
highly skilled. Many jazz musicians prefer to improvise in small, highly skilled
teams, such as jazz quartets. To improvise effectively, the musicians must have
a thorough understanding of the conventions that form the given musical style,
including chord sequences, rhythmic patterns, and melodies. These conventions
provide a basic framework for the musicians to interact as a team, while still
allowing room for spontaneous creativity. &lt;/p&gt;
&lt;p&gt; Likewise, use cases do not always need to be specified in excruciating detail.
A far-preferable strategy is simply to define the basic structure of what the
developers need to implement. The use cases act as placeholders that may be
elaborated later or simply improvised by the developer who implements the use
case. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Forces:&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Briefs do not provide enough information. &lt;/strong&gt;While useful,
use-case briefs describe only the more significant parts of behavior. Often,
developers need more information, especially when working in unfamiliar
domains or in the heart of the system, where the actor has many choices
to make and many paths to follow. Briefs do not describe all of the important
events that can happen, nor do they describe the details that go into making
choices along the way. &lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Fully elaborated use cases can be too expensive, time consuming,
long to write, and boring to read. &lt;/strong&gt;It
takes a lot of time and effort to write a formal, fully descriptive set
of use cases. Maintaining this set takes even longer. Often, a collection
of use cases reaches the point of diminishing returns long before it is
completely written, much less formalized. Readers often prefer shorter,
simpler use cases over long, complicated ones, because overly detailed use
cases can be overwhelming and, frankly speaking, quite boring. &lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Many groups communicate well enough to
resolve ambiguities on the fly. &lt;/strong&gt;While briefs may be insufficient,
stakeholders don’t always need everything to be spelled out for them. Developers
are usually capable of asking questions and filling out the necessary detail
from their own domain knowledge. Many people can work with a fair level
of ambiguity, and most organizations possess what is often referred to as
their “core competencies.” Mature organizations with strong domain knowledge
can survive, and even thrive, using more informal, less precise use cases.
&lt;p&gt; &lt;strong&gt;Solution: &lt;/strong&gt;Specify the use cases at
a low level of precision, allowing the developers to fill in the missing details
as necessary. The level of precision required depends on the background experiences
of the development team. Skip the less meaningful fields on the template, and
write the Main Scenario section as a simple paragraph.
Describe key-extension handling in the next paragraph
or two. Be prepared to resolve ambiguities and expand detail on the fly throughout
the project. &lt;/p&gt;
&lt;p&gt; When you can rely upon open and frequent communication among the developers
and customer, write the use case with less detail and precision. The developers
can fill in the gaps by asking users or by using knowledge of the domain. However,
the developers need a thorough understanding of the business context to be able
to fill out the details themselves. Even the most knowledgeable developer will
still need access to the customers and users to get answers to questions and
clarify requirements. &lt;/p&gt;
&lt;p&gt; Ideally, the project will be structured to enable effective communication
between the customer and the developers. Typically, this will involve having
a small, co-located team, with the developers having easy access to the users
throughout the project. The risk of misunderstanding can be resolved by frequent
incremental delivery if the development organization
has a relatively low-ceremony culture. &lt;/p&gt;
&lt;p&gt; Jazz improvisation does not always work. It can become tedious and unpleasant
to listen to, even for the committed connoisseur.
For this reason, you also need feedback from the audience to determine the success
of the improvisations. Multi-level or two-tier reviews are critical to success
(see &lt;a class=&quot;elementLinkWithType&quot; href=&quot;./../../../openup_basic/guidances/guidelines/effective_req_reviews,_E-dPIL-GEdqb7N6KIeDL8Q.html&quot; guid=&quot;_E-dPIL-GEdqb7N6KIeDL8Q&quot;&gt;Guideline:
Effective Requirement Reviews&lt;/a&gt;). &lt;/p&gt;
&lt;p&gt; Improvisation may not always be suitable for the organizational culture, a
full &lt;strong&gt;symphonic score&lt;/strong&gt; may be preferable in large, high-ceremony
teams (see section that follows). For instance,
I once watched a conductor toss his baton away in disgust when a pianist improvised
to such an extent that the orchestra could not follow the score. If the organization
deems the risk of improvising to be unacceptably high, then you can specify
the use cases with a higher level of detail and precision. You could start with
a strategy of specifying low levels of detail and precision, and then adapt
as necessary. &lt;/p&gt;
&lt;h4&gt; Symphonic score &lt;/h4&gt;
&lt;p&gt; &lt;strong&gt;Context: &lt;/strong&gt;Writing structure for high-ceremony situations,
such as when there are many developers or when development teams are geographically
dispersed. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Problem: &lt;/strong&gt;Writing low-ceremony use cases for high-ceremony
situations raises the risk of miscommunication to unacceptable levels. &lt;/p&gt;
&lt;p&gt; A conductor’s version of a symphonic score contains the music for the entire
orchestra, as well as any accompanying vocals. The parts to be performed by
different voices or instruments are written on a separate staff, with all of
the staves aligned, one above another. This score specifies each note and its
associated timing in precise detail, so that the orchestra can perform a symphony
as the composer intended. &lt;/p&gt;
&lt;p&gt; As with use cases, a score tells the musician what to play, not how to play
it. For most symphonies, the orchestra will not be able to meet the composer,
so instead, they must rely upon the director to interpret the
score and the composer's intentions. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Forces: &lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Certain development situations and cultures require high degrees
of formality. &lt;/strong&gt;Some organizations operate in a highly formal manner,
thus require a highly formal process. While this formality may not
be desirable, it is the company's way of doing business, so things need
to be done that way. Other organizations are highly formal because they
do highly complex, life-critical work, where even small failures could have
disastrous consequences. For instance, no one would feel comfortable flying
on an airliner with an off-the-shelf, one-size-fits-all flight management
system. &lt;/p&gt;
&lt;p&gt;&lt;strong&gt;The cost of repairing miscommunication
is high. &lt;/strong&gt;It is easy to write vague, inadequate use cases full of
ambiguity. Use cases can be too brief and ambiguous, or contain domain-specific
details that may be beyond the understanding of many stakeholders. Either
way, they provide an opportunity for a misunderstanding that leads to an
incorrect implementation. The cost of correcting these mistakes depends
on when they are discovered. &lt;em&gt;Earlier&lt;/em&gt; is cheaper than&lt;em&gt; later&lt;/em&gt;,
especially when later means customers finding the problem in the delivered
product. To avoid miscommunication, aim to write use cases that are general
enough for all of the stakeholders to follow, yet precise enough for the
developers to use when building the system. &lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Developers need detail for implementing steps, business rules,
data fields, and, especially, for handling extensions. &lt;/strong&gt;No one has
developed a program that can take a set of use cases as input, and churn
out a completed system. Even the best-case tools seem to require human intervention
to flesh out details and resolve ambiguities. Similarly, developers who
do not understand the business context or lack domain expertise may not
be able to fully comprehend a product. In an ideal project, software developers
would have access to the domain experts to ask questions, so they could
fill in any areas that may have been missed (see&lt;em&gt; Improvisational score&lt;/em&gt;,
previously). But often, they do not ask. Therefore, they misunderstand the
more complex or ambiguous use cases in the set. To develop a system correctly,
a team needs either access to domain experts or additional information that
describe the steps, business rules, data fields, and extension handling
that they are implementing. &lt;/p&gt;
&lt;p&gt; &lt;strong&gt;Solution: &lt;/strong&gt;Specify your use cases with a high level of precision,
explicitly filling in all of the details in the use case template, while staying
technology-neutral. The level of precision required depends on the background
experiences of the development team. &lt;/p&gt;
&lt;p&gt; Intuition may tell you that if some detail is good, then more must be better.
However, be careful about falling into the trap of over-specifying details.
It’s naive to believe that everyone who reads your use cases will be able to
understand them. Different people may interpret the use cases differently. Prepare
for this eventuality in your process, and avoid the tendency to over-specify
your use cases. If you try to specify a use case in too much detail, you may
fall into the classic analysis paralysis trap. &lt;/p&gt;
&lt;p&gt; People are often tempted to address the communication problem by trying to
explain the business domain within the use cases. In a similar manner, they
include too much technical detail. Succumbing to these temptations by explaining
the business domain or including technical details is always a mistake, because
it complicates the process and obfuscates the requirements. The reader of the
use cases cannot distinguish the real requirements from the boring background
information, so will soon get distracted and lose interest. Instead, include
this information in an extra section. &lt;/p&gt;
&lt;p&gt; If you are handing over the requirements to a development team whose members
are unfamiliar with the domain, then you will need an alternative strategy for
teaching them the domain knowledge. &lt;/p&gt;</mainDescription>