A software requirement specifies a need to be fulfilled by the software product.

A software project may be,

• a brown-field project i.e., develop a product to replace/update an existing software product
• a green-field project i.e., develop a totally new system with no precedent

In either case, requirements need to be gathered, analyzed, specified, and managed.

Requirements come from stakeholders.

Identifying requirements is often not easy. For example, stakeholders may not be aware of their precise needs, may not know how to communicate their requirements correctly, may not be willing to spend effort in identifying requirements, etc.

There are two kinds of requirements:

1. Functional requirements specify what the system should do.
2. Non-functional requirements specify the constraints under which system is developed and operated.

We should spend extra effort in digging NFRs out as early as possible because NFRs are easier to miss  e.g., stakeholders tend to think of functional requirements first and sometimes they are critical to the success of the software.  E.g. A web application that is too slow or that has low security is unlikely to succeed even if it has all the right functionality.

Requirements can be prioritized based the importance and urgency, while keeping in mind the constraints of schedule, budget, staff resources, quality goals, and other constraints.

A common approach is to group requirements into priority categories. Note that all such scales are subjective, and stakeholders define the meaning of each level in the scale for the project at hand.

Some requirements can be discarded if they are considered ‘out of scope’.

Here are some characteristics of well-defined requirements ^{[📖 zielczynski]}:

• Unambiguous
• Testable (verifiable)
• Clear (concise, terse, simple, precise)
• Correct
• Understandable
• Feasible (realistic, possible)
• Independent
• Atomic
• Necessary
• Implementation-free (i.e. abstract)

Besides these criteria for individual requirements, the set of requirements as a whole should be

• Consistent
• Non-redundant
• Complete

In a brainstorming session there are no "bad" ideas. The aim is to generate ideas; not to validate them. Brainstorming encourages you to "think outside the box" and put "crazy" ideas on the table without fear of rejection.

Studying existing products can unearth shortcomings of existing solutions that can be addressed by a new product. Product manuals and other forms of technical documentation of an existing system can be a good way to learn about how the existing solutions work.

Observing users in their natural work environment can uncover product requirements. Usage data of an existing system can also be used to gather information about how an existing system is being used, which can help in building a better replacement  e.g. to find the situations where the user makes mistakes when using the current system.

Surveys can be used to solicit responses and opinions from a large number of stakeholders regarding a current product or a new product.

Interviewing stakeholders and domain experts can give us useful information that project requirements.

Focus groups are a kind of informal interview within an interactive group setting. A group of people (e.g. potential users, beta testers) are asked about their understanding of a specific issue, process, product, advertisement, etc.

Prototyping can uncover requirements, in particular, those related to how users interact with the system. UI prototypes are often used in brainstorming sessions, or in meetings with the users to get quick feedback from them.

^{[source: http://balsamiq.com/products/mockups]}

💡 Prototyping can be used for discovering as well as specifying requirements  e.g. a UI prototype can serve as a specification of what to build.

A normal textual description (i.e. prose) can be used to describe requirements. Prose is especially useful when describing abstract ideas such as the vision of a product.

❗️ Avoid using lengthy prose to describe requirements; they can be hard to follow.

A common format for writing user stories is:

We can write user stories on index cards or sticky notes, and arrange on walls or tables, to facilitate planning and discussion. Alternatively, we can use a software (e.g., GitHub Project Boards, Trello, Google Docs, ...) to manage user stories digitally.

^{[credit: https://www.flickr.com/photos/jakuza/2682466984/]}

^{[credit: https://www.flickr.com/photos/jakuza/with/2726048607/]}

^{[credit: https://commons.wikimedia.org/wiki/File:User_Story_Map_in_Action.png]}

The {benefit} can be omitted if it is obvious.

❗️ It is recommended to confirm there is a concrete benefit even if you omit it from the user story. If not, we could end up adding features that have no real benefit.

We can add more characteristics to the {user role} to provide more context to the user story.

We can write user stories at various levels. High-level user stories, called epics (or themes) cover bigger functionality. We can then break down these epics to multiple user stories of normal size.

We can add conditions of satisfaction to a user story to specify things that need to be true for the user story implementation to be accepted as ‘done’.

Other useful info that can be added to a user story includes (but not limited to)

• Priority: how important the user story is
• Size: the estimated effort to implement the user story
• Urgency: how soon the feature is needed

User stories capture user requirements in a way that is convenient for scoping, estimation and scheduling.

[User stories] strongly shift the focus from writing about features to discussing them. In fact, these discussions are more important than whatever text is written. _{[Mike Cohn, MountainGoat Software 🔗]}

User stories differ from traditional requirements specifications mainly in the level of detail. User stories should only provide enough details to make a reasonably low risk estimate of how long the user story will take to implement. When the time comes to implement the user story, the developers will meet with the customer face-to-face to work out a more detailed description of the requirements. [more...]

User stories can capture non-functional requirements too because even NFRs must benefit some stakeholder.

While use cases can be recorded on physical paper in the initial stages, an online tool is more suitable for longer-term management of user stories, especially if the team is not co-located.

A use case describes an interaction between the user and the system for a specific functionality of the system.

UML includes a diagram type called use case diagrams that can illustrate use cases of a system visually, providing a visual ‘table of contents’ of the use cases of a system. In the example below, note how use cases are shown as ovals and user roles relevant to each use case are shown as stick figures connected to the corresponding ovals.

Use cases capture the functional requirements of a system.

A use case is an interaction between a system and its actors.

Actors in Use Cases

A use case can involve multiple actors.

An actor can be involved in many use cases.

A single person/system can play many roles.

Many persons/systems can play a single role.

Use cases can be specified at various levels of detail.

Writing use case steps

Extensions are "add-on"s to the MSS that describe exceptional/alternative flow of events. They describe variations of the scenario that can happen if certain things are not as expected by the MSS. Extensions appear below the MSS.

This example adds some extensions to the use case in the previous example.

• System: Online Banking System (OBS)
• Use case: UC23 - Transfer Money
• Actor: User
• MSS:
  1. User chooses to transfer money.
  2. OBS requests for details of the transfer.
  3. User enters the requested details.
  4. OBS requests for confirmation.
  5. OBS transfers the money and displays the new account balance.
  6. Use case ends.
• Extensions:
  1. 3a. OBS detects an error in the entered data.
     1. 3a1. OBS requests for the correct data.
     2. 3a2. User enters new data.
     3. Steps 3a1-3a2 are repeated until the data entered are correct.
     4. Use case resumes from step 4.
  2. 3b. User requests to effect the transfer in a future date.
     1. 3b1. OBS requests for confirmation.
     2. 3b2. User confirms future transfer.
     3. Use case ends.
  3. *a. At any time, User chooses to cancel the transfer.
     1. *a1. OBS requests to confirm the cancellation.
     2. *a2. User confirms the cancellation.
     3. Use case ends.
  4. *b. At any time, 120 seconds lapse without any input from the User.
     1. *b1. OBS cancels the transfer.
     2. *b2. OBS informs the User of the cancellation.
     3. Use case ends.

Note that the numbering style is not a universal rule but a widely used convention. Based on that convention,

• either of the extensions marked 3a. and 3b. can happen just after step 3 of the MSS.
• the extension marked as *a. can happen at any step (hence, the *).

When separating extensions from the MSS, keep in mind that the MSS should be self-contained. That is, the MSS should give us a complete usage scenario.

Also note that it is not useful to mention events such as power failures or system crashes as extensions because the system cannot function beyond such catastrophic failures.

In use case diagrams you can use the << extend >> arrows to show extensions. Note the direction of the arrow is from the extension to the use case it extends and the arrow uses a dashed line.

A use case can include another use case. Underlined text is commonly used to show an inclusion of a use case.

This use case includes two other use cases, one in step 1 and one in step 2.

• Software System: LearnSys
• Use case: UC01 - Conduct Survey
• Actors: Staff, Student
• MSS:
  1. Staff creates the survey (UC44).
  2. Student completes the survey (UC50).
  3. Staff views the survey results.
  4. Use case ends.

Inclusions are useful,

• when you don't want to clutter a use case with too many low-level steps.
• when a set of steps is repeated in multiple use cases.

We use a dotted arrow and a << include >> annotation to show use case inclusions in a use case diagram. Note how the arrow direction is different from the << extend >> arrows.

You can use actor generalization in use case diagrams using a symbol similar to that of UML notation for inheritance.

In this example, actor Blogger can do all the use cases the actor Guest can do, as a result of the actor generalization relationship given in the diagram.

💡 Do not over-complicate use case diagrams by trying to include everything possible. A use case diagram is a brief summary of the use cases that is used as a starting point. Details of the use cases can be given in the use case descriptions.

Some include ‘System’ as an actor to indicate that something is done by the system itself without being initiated by a user or an external system.

The diagram below can be used to indicate that the system generates daily reports at midnight.

However, others argue that only use cases providing value to an external user/system should be shown in the use case diagram. For example, they argue that ‘view daily report’ should be the use case and generate daily report is not to be shown in the use case diagram because it is simply something the system has to do to support the view daily report use case.

We recommend that you follow the latter view (i.e. not to use System as a user). Limit use cases for modeling behaviors that involve an external actor.

UML is not very specific about the text contents of a use case. Hence, there are many styles for writing use cases. For example, the steps can be written as a continuous paragraph. Use cases should be easy to read. Note that there is no strict rule about writing all details of all steps or a need to use all the elements of a use case.

There are some advantages of documenting system requirements as use cases:

• Because they use a simple notation and plain English descriptions, they are easy for users to understand and give feedback.
• They decouple user intention from mechanism (note that use cases should not include UI-specific details), allowing the system designers more freedom to optimize how a functionality is provided to a user.
• Identifying all possible extensions encourages us to consider all situations that a software product might face during its operation.
• Separating typical scenarios from special cases encourages us to optimize the typical scenarios.

One of the main disadvantages of use cases is that they are not good for capturing requirements that does not involve a user interacting with the system. Hence, they should not be used as the sole means to specify requirements.

A supplementary requirements section can be used to capture requirements that do not fit elsewhere. Typically, this is where most Non Functional Requirements will be listed.

Javadoc is a tool for generating API documentation in HTML format from doc comments in source. In addition, modern IDEs use JavaDoc comments to generate explanatory tool tips.

/**
 * Returns an Image object that can then be painted on the screen. 
 * The url argument must specify an absolute {@link URL}. The name
 * argument is a specifier that is relative to the url argument. 
 * <p>
 * This method always returns immediately, whether or not the 
 * image exists. When this applet attempts to draw the image on
 * the screen, the data will be loaded. The graphics primitives 
 * that draw the image will incrementally paint on the screen. 
 *
 * @param url an absolute URL giving the base location of the image
 * @param name the location of the image, relative to the url argument
 * @return the image at the specified URL
 * @see Image
 */
 public Image getImage(URL url, String name) {
        try {
            return getImage(new URL(url, name));
        } catch (MalformedURLException e) {
            return null;
        }
 }

{to add}

Markdown is a lightweight markup language with plain text formatting syntax.

...

AsciiDoc is similar to Markdown but has more powerful (but also more complex) syntax.

Well-written applications include error-handling code that allows them to recover gracefully from unexpected errors. When an error occurs, the application may need to request user intervention, or it may be able to recover on its own. In extreme cases, the application may log the user off or shut down the system. --_(source)

Exceptions are used to deal with 'unusual' but not entirely unexpected situations that the program might encounter at run time.

Most languages allow a method/function to encapsulate the unusual situation in an Exception object and 'throw'/'raise' that object so that another piece of code can 'catch' it and deal with it. This is especially useful when code segment that encountered the unusual situation does not know how to deal with it.

Exception objects can propagate up the function call hierarchy until it is dealt with. Usually, an exception thrown by a function is caught by the caller function. If the called function does not know how to deal with the exception it caught, it can throw/raise the Exception object to its own caller. If none of the callers is prepared to deal with the exception, the exceptions can propagate through the function call stack until it is received by the main function and thrown to the runtime, thus halting the system.

In the code given below, processArray can potentially throw an InvalidInputException. Because of that, processInput method invokes processArray method inside a try{ } block and has a catch{ } block to specify what to do if the exception is actually thrown.

In the code given below, process_array function can potentially raise a ValueError exception. Because of that, process_input function invokes process_array function inside a try clause and has a except clause to specify what to do if the exception is actually raised.

Advantages of exception handling in this way:

• The ability to propagate error information through the call stack.
• The separation of code that deals with 'unusual' situations from the code that does the 'usual' work.

In general, use exceptions only for 'unusual' conditions. Use normal return statements to pass control to the caller for conditions that are 'normal'.

Branching is the process of evolving multiple versions of the software in parallel. For example, one team member can create a new branch and add an experimental feature to it while the rest of the team keeps working on another branch. Branches can be given names e.g. master release dev.

A branch can be merged into another branch. Merging usually result in a new commit that represents the changes done in the branch being merged.

Merge conflicts happen when you try to merge two branches that had changed the same part of the code and the RCS software cannot decide which changes to keep. In those cases we have to ‘resolve’ those conflicts manually.

0. Observe that you are normally in the branch called master. For this, you can take any repo you have on your computer (e.g. a clone of the samplerepo-things).

---

git status

on branch master

---

1. Start a branch named feature1 and switch to the new branch.

Click on the Branch button on the main menu. In the next dialog, enter the branch name and click Create Branch

Note how the feature1 is indicated as the current branch.

---

You can use the branch command to create a new branch and the checkout command to switch to a specific branch.

git branch feature1
git checkout feature1

One-step shortcut to create a branch and switch to it at the same time:

git checkout –b feature1

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2. Create some commits in the new branch. Just commit as per normal. Commits you add while on a certain branch will become part of that branch.

3. Switch to master branch. Note how the changes you did in the feature1 branch are no longer in the working directory.

Double-click the master branch

---

git checkout master

---

4. Add a commit to the master branch. Let’s imagine it’s a bug fix.

5. Switch back to the feature1 branch (similar to step 3).

6. Merge the master branch to the feature1 branch, giving an end-result like the below. Also note how Git has created a merge commit.

git merge master

Observe how the changes you did in the master branch (i.e. the imaginary bug fix) is now available even when you are in the feature1 branch.

7. Add another commit to the feature1 branch.

8. Switch to the master branch and add one more commit.

9. Merge feature1 to the master branch, giving and end-result like this:

git merge feature1

10. Create a new branch called add-countries, switch to it, and add some commits to it (similar to steps 1-2 above). You should have something like this now:

11. Go back to the master branch and merge the add-countries branch onto the master branch (similar to steps 8-9 above). While you might expect to see something like the below,

... you are likely to see something like this instead:

That is because Git does a fast forward merge if possible. Seeing that the master branch has not changed since you started the add-countries branch, Git has decided it is simpler to just put the commits of the add-countries branch in front of the master branch, without going into the trouble of creating an extra merge commit.

It is possible to force Git to create a merge commit even if fast forwarding is possible.

Tick the box shown below when you merge a branch:

---

Use the --no-ff switch (short for no fast forward):

git merge --no-ff add-countries

---

1. Fork the samplerepo-pr-practice onto your GitHub account. Clone it onto your computer.

2. Create a branch named add-intro in your clone. Add a couple of commits which adds/modifies an Introduction section to the README.md. Example:

# Introduction
Creating Pull Requsts (PRs) is needed when using RCS in a multi-person projects.
This repo can be used to practice creating PRs.

3. Push the add-intro branch to your fork.

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git push origin add-intro

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4. Create a Pull Request from the add-intro branch in your fork to the master branch of the same fork (i.e. your-user-name/samplerepo-pr-practice, not se-edu/samplerepo-pr-practice), as described below.

4a. Go to the GitHub page of your fork (i.e. https://github.com/{your_username}/samplerepo-pr-practice), click on the Pull Requests tab, and then click on New Pull Request button.

4b. Select base fork and head fork as follows:

• base fork: your own fork (i.e. {your user name}/samplerepo-pr-practice, NOT se-edu/samplerepo-pr-practice)
• head fork: your own fork.

4c. (1) Set the base branch to master and head branch to add-intro, (2) confirm the diff contains the changes you propose to merge in this PR (i.e. confirm that you did not accidentally include extra commits in the branch), and (3) click the Create pull request button.

4d. (1) Set PR name, (2) set PR description, and (3) Click the Create pull request button.

5. In your local repo, create a new branch add-summary off the master branch.

6. Add a commit in the add-summary branch that adds a Summary section to the README.md, in exactly the same place you added the Introduction section earlier.

7. Push the add-summary to your fork and create a new PR similar to before.