Skip to main content

Translating requirements into system design - A case study

In this section we will take a requirements document for a software system and create a system design from it. The statement for the excercise has been inspired by Dave Thomas' coding kata #1. Let's build a system for a supermarket. Here are the requirements.

The supermarket has various items for selling. Each item has a price. Sometimes an item may have a discounted price, and sometimes it may be part of a scheme. Schemes could be similar to buy two get one free, or buy a certain quantity of an item and get another item free. Items may also be priced for a certain unit. For example Apples may be Rs 40/Kg, however they can be sold in a fractional unit also 500 gms. Some items may be simple, like a can of Pepsi or complex like a crate of 10 Pepsi cans. The sytem should also maintain an audit trail of all sold items for future evaluation.

The store manager should be able to get a valuation of the current stock.

When a shopper checks out items the system should calculate the most optimum price based on schemes that the items may be part of.

Please Note: To keep the exercise simple we do not concerning ourselves with inventory. We only consider items and pricing.

Here are the use cases for this exercise.

supermarket_usecases.gif 

Resources:

  1. Dave Thomas' coding kata's 

Comments

Popular posts from this blog

Commenting your code

Comments are an integral part of any program, even though they do not contribute to the logic. Appropriate comments add to the maintainability of a software. I have heard developers complain about not remembering the logic of some code they wrote a few months back. Can you imagine how difficult it can be to understand programs written by others, when we sometimes find it hard to understand our own code. It is a nightmare to maintain programs that are not appropriately commented. Java classes should contain comments at various levels. There are two types of comments; implementation comments and documentation comments. Implementation comments usually explain design desicisions, or a particularly intricate peice of code. If you find the need to make a lot of implementation comments, then it may signal overly complex code. Documentation comments usually describe the API of a program, they are meant for developers who are going to use your classes. All classes, methods and variables ...

Inheritance vs. composition depending on how much is same and how much differs

I am reading the excellent Django book right now. In the 4th chapter on Django templates , there is an example of includes and inheritance in Django templates. Without going into details about Django templates, the include is very similar to composition where we can include the text of another template for evaluation. Inheritance in Django templates works in a way similar to object inheritance. Django templates can specify certain blocks which can be redefined in subtemplates. The subtemplates use the rest of the parent template as is. Now we have all learned that inheritance is used when we have a is-a relationship between classes, and composition is used when we have a contains-a relationship. This is absolutely right, but while reading about Django templates, I just realized another pattern in these relationships. This is really simple and perhaps many of you may have already have had this insight... We use inheritance when we want to allow reuse of the bulk of one object in other ...

Planning a User Guide - Part 3/5 - Co-ordinate the Team

Photo by  Helloquence  on  Unsplash This is the third post in a series of five posts on how to plan a user guide. In the first post , I wrote about how to conduct an audience analysis and the second post discussed how to define the overall scope of the manual. Once the overall scope of the user guide is defined, the next step is to coordinate the team that will work on creating the manual. A typical team will consist of the following roles. Many of these roles will be fulfilled by freelancers since they are one-off or intermittent work engagements. At the end of the article, I have provided a list of websites where you can find good freelancers. Creative Artist You'll need to work with a creative artist to design the cover page and any other images for the user guide. Most small to mid-sized companies don't have a dedicated creative artist on their rolls. But that's not a problem. There are several freelancing websites where you can work with great creative ...