computer science

Use case points

Use case points is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Use case points rather than just read about it. In short: Use case points (UCP or UCPs) is a software estimation technique used to forecast the software size for software development projects. UCP is used when the Unified Modeling Language (UML) and Rational Unified Process (RUP) methodologies are being used for the software design and development.

Key takeaways

Use case points belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Use case points to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Use case points from memory before moving on to harder problems.

Reference excerpt

Use case points (UCP or UCPs) is a software estimation technique used to forecast the software size for software development projects. UCP is used when the Unified Modeling Language (UML) and Rational Unified Process (RUP) methodologies are being used for the software design and development. The concept of UCP is based on the requirements for the system being written using use cases, which is part of the UML set of modeling techniques. The software size (UCP) is calculated based on elements of the system use cases with factoring to account for technical and environmental considerations. The UCP for a project can then be used to calculate the estimated effort for a project.

History The UCP technique was developed by Gustav Karner in 1993 while employed at what was known at the time as Objectory Systems, which later merged into Rational Software and then IBM. The UCP method was created to solve for estimating the software size of systems that were object oriented. It is based on similar principles as the Function Point (FP) estimation method, but was designed for the specific needs of object oriented systems and system requirements based on use cases.

Method The method for determining the size estimate to develop a system is based on a calculation with the following elements:

Unadjusted Use Case Weight (UUCW) – the point size of the software that accounts for the number and complexity of use cases. Unadjusted Actor Weight (UAW) – the point size of the software that accounts for the number and complexity of actors. Technical Complexity Factor (TCF) – factor that is used to adjust the size based on technical considerations. Environmental Complexity Factor (ECF) – factor that is used to adjust the size based on environmental considerations. Once the previous four elements have been calculated, the final size estimate can be calculated. This final number is known as the use case points or UCP for a software development project. The following sections walk through the various calculations to determine the UCP for a project.

Unadjusted Use Case Weight (UUCW) The UUCW is one of the factors that contribute to the size of the software being developed. It is calculated based on the number and complexity of the use cases for the system. To find the UUCW for a system, each of the use cases must be identified and classified as Simple, Average or Complex based on the number of transactions the use case contains. Each classification has a predefined weight assigned. Once all use cases have been classified as simple, average or complex, the total weight (UUCW) is determined by summing the corresponding weights for each use case. The following chart shows the different classifications of use cases based on the number of transactions and the weight value assigned for each use case within the classification.

UUCW = (Total No. of Simple Use Cases x 5) + (Total No. Average Use Cases x 10) + (Total No. Complex Use Cases x 15)

Unadjusted Actor Weight (UAW) The UAW is another factor that contributes to the size of the software being developed. It is calculated based on the number and complexity of the actors for the system. Similar to finding the UUCW, each of the actors must be identified and classified as Simple, Average or Complex based on the type of actor. Each classification also has a predefined weight assigned. The UAW is the total of the weights for each of the actors. The following chart shows the different classifications of actors and the weight value assigned.

UAW = (Total No. of Simple actors x 1) + (Total No. Average actors x 2) + (Total No. Complex actors x 3)

Technical Complexity Factor (TCF) The TCF is one of the factors applied to the estimated size of the software in order to account for technical considerations of the system. It is determined by assigning a score between 0 (factor is irrelevant) and 5 (factor is essential) to each of the 13 technical factors listed in the table below. This score is then multiplied by the defined weighted value for each factor. The total of all calculated values is the technical factor (TF). The TF is then used to compute the TCF with the following formula:

TCF = 0.6 + (TF/100)

Environmental Complexity Factor (ECF) The ECF is another factor applied to the estimated size of the software in order to account for environmental considerations of the system. It is determined by assigning a score between 0 (no experience) and 5 (expert) to each of the 8 environmental factors listed in the table below. This score is then multiplied by the defined weighted value for each factor. The total of all calculated values is the environment factor (EF). The EF is then used to compute the ECF with the following formula:

ECF = 1.4 + (-0.03 x EF)

Use Case Points (UCP) Finally the UCP can be calculated once the unadjusted project size (UUCW and UAW), technical factor (TCF) and environmental factor (ECF) have been determined. The UCP is calculated based on the following formula:

UCP = (UUCW + UAW) x TCF x ECF

Example To illustrate the process of calculating the UCP, an Online Shopping System will be used. The diagram below depicts the Use Case Diagram for the system to be developed.

Unadjusted Use Case Weight (UUCW) To calculate the UUCW, the use cases must be defined and the number of transactions for each use case identified. The Online Shopping System use case diagram is depicting that nine use cases exist for the system. Assuming 2 of these use cases are simple, 3 are average and 4 are complex, the calculation for UUCW is as follows:

UUCW = (Total No. of Simple Use Cases x 5) + (Total No. Average Use Cases x 10) + (Total No. Complex Use Cases x 15) For the Online Shopping System, the UUCW = (2 x 5) + (3 x 10) + (4 x 15) = 100 UUCW = 100

Unadjusted Actor Weight (UAW) To calculate the UAW, the actors must be identified. The Online Shopping System use case diagram is depicting five actors; One simple for the Payment Processing System and four complex for each of the human users actors (i.e. Online Customer, Marketing Administrator, Warehouse Clerk, Warehouse Manager.) The calculation for UAW is as follows:

UAW = (Total No. of Simple Actors x 1) + (Total No. Average Actors x 2) + (Total No. Complex Actors x 3) For the Online Shopping System, UAW = (1 x 1) + (0 x 2) + (4 x 3) = 13 UAW = 13

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Use case points

Start with the simplest possible case. Write down what Use case points claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Use case points before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Use case points ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Use case points

In research: Use case points appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Use case points in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Use case points is common in secondary-school and first-year university syllabi. It links to neighbouring topics Software engineering costs, Software metrics, so understanding it makes those chapters shorter.
In everyday life: Look for Use case points outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Use case points in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Use case points means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Use case points out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Use case points in simple terms?

Why does Use case points matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Use case points?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Use case points.