Unified Modeling Language (UML)

I like use cases. There, I said it, and I’m not sorry. Use cases have fallen out of fashion in recent years, being largely replaced by user stories on agile projects. The two techniques can coexist and complement each other, however.  Use cases offer several advantages that user stories lack. This article describes some of the many benefits that use cases can provide and why every business analyst (BA), product owner (PO), and software development team should include them in their tool kit.

Although use cases are valuable for many projects, sometimes event analysis is a more effective requirements elicitation technique. Valuable as they are, use cases aren’t the ideal tool for every type of product. A complementary requirements elicitation strategy is to explore the various events that a system or product could experience and how it should respond to each of them. The response depends on what state the system is in when it detects the event. Event analysis is particularly well-suited for middleware products and real-time systems that include both software and hardware components.

What is Use Case?

Use case represents requirement in the form of user interactions with the system. Use case is always written with a specific user goal in mind. Each use case must contain an actor and verb. For example, ‘online buyer’ is an actor and ‘add item to cart’ is a verb.

A use case diagram represents the scope of all the features of the solution. It follows Unified Modelling Language™ notation. Use case diagram comprises of several use cases that make the system altogether.

What is User Story?

User story is a business analysis artifact that is also user or persona driven. It describes the business need in the form of an ability user (or system) wants in the solution. It also must state why the ability is required and what the benefits of that ability are. It does not have any mandatory format though

User story is part of the (product/project) backlog. The backlog in turn contains user stories/tasks (requirements) in a linear fashion. Backlog is usually prioritized from high to low, additionally with a ranking when priorities are the same. When it is prioritized by business value of the tasks/stories in it, it is called managed backlog. In many projects, user stories are also represented visually as a user story map, which is a structured visualization of a backlog. User story map is a map of user stories that are transposed from a linear backlog, onto a visual working board.

Each of this concept is a detailed topic in itself. For the context of this article, I will limit it only at the introductory level. Let's now look into differences and similarities between user stories and use cases.

A diagram is a 2-dimensional representation of a story, which shows elements and their relationships on a single canvas. An element is shown on a single diagram. (To show the same element information on a 2 diagrams, the element is duplicated.) When the properties of a diagram element are changed, the change is reflected only on that diagram.

A model is a 3-dimensional representation of a collection of related stories, which captures diagram elements as model components. A component includes all element properties and relationships between different elements on all diagrams. A single model component can be shown as elements on several diagrams. A change to the properties of a diagram element or model component is reflected on every diagram where that component is displayed.

A model does not necessarily need to include any diagrams. Diagramming is the most common method for creating and maintaining model components, but the diagrams can be deleted without changing the model.

If a picture is worth a thousand words, then a diagram converts those words into a story. A model organizes those stories into a book.

So how do you handle CRUD in your use cases? Please don’t confuse CRUD with CRAP in your use cases. That’s a lot harder to deal with and requires a conversation with your subject matter experts (SMEs). CRUD is an acronym for Create, Read, Update and Delete. It describes the lifecycle in the maintenance of system data, whether that data is stored in a database or is file based data stored in a document management system like SharePoint.

In the world of software development Use Cases are one of many very powerful techniques often used these days.  Use cases describe how a person or a system interacts with the solution being modeled/built to achieve a goal. Basically, it’s a step by step explanation of what a user can do and how the solution must respond.

As any other business analysis technique, use cases have their advantages and disadvantages. One of the main disadvantages of use cases is that this technique is not graphical – a use case diagram is but use case descriptions are not, and use case descriptions really lack of visualization especially if there are multiple alternative flows and exception flows that branch out and then loop back into the main one.

Visual analysis models provide a powerful set of tools that let business analysts depict system information at various levels of abstraction. These models serve as an aid to understanding, as well as an aid to communicating. Alas, I fear that modeling is somewhat of a neglected practice. I believe modeling is an essential skill every BA should master. Here’s why.

Several years ago I was looking for examples using the generalization / specialization technique with use cases. They are not easier to find. And they are typically limited to a use case diagram like the two below. This article provides examples of both the diagrams and the scenarios for a future gas station business.

Strategists, architects, process experts, software developers, data managers and other professionals involved in changing the enterprise often put substantial effort in creating all kinds of useful models of their designs. In many cases, such business models, enterprise architecture models, business process models, software models, or data models are only used to specify some design, i.e. to describe what should be built. 
But there is much more value to be had from these models, by using powerful analysis techniques to elicit new insights. In the following pages I will cover 7 of these analyses, discussing the business outcomes you can achieve with their help.

State Models include two RML Data models (State Tables and State Diagrams) that show the transition of an object through various states or statuses, including which transitions are valid and what triggers an object to transition state. A state is a short-form description of a stage in a data object’s life that influences the behavior of the system.

The problem with many Unified Modeling Language (UML) educational texts is that they present the various concepts each in isolation; so you see a use case diagram for one problem domain, a class diagram for an entirely different problem domain, and you never get to see the important traceability between the diagrams.

In this case study we aim to put it right by working through a single problem from use cases and activity diagrams, through sequence diagrams and state diagrams, to class diagrams and component diagrams. We have arranged the case study as three distinct perspectives or aspects as follows.

The UML Component Diagram along with the complementary UML Deployment Diagram shows how a software solution will be delivered and deployed in the form of interconnected components that interoperate via well-defined interfaces. You can think of this as analogous to how electronic components are wired together, and in this context you should consider that any one component may be replaced by a different but compatible component with no adverse effect.

The UML State Diagram, sometimes known as the Statechart Diagram or Static Transition Diagram, defines the entire lifecycle of a business entity or object in terms of the messages it receives and the responses it makes from the moment of creation until the moment of destruction.

A UML Use Case is an atomic system function with a well-defined and standardized specification, which is performed by or o behalf of a system user or ‘actor’. This article describes how a UML Use Case Specification should be written.