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System Interactions (Use Cases)

Top level requirements are collected during an interactive facilitated session with the key stakeholders. Here, the starting point is a discussion of the high-level events that cause a stakeholder to interact with (use) the system. This approach is conducted in non-technical, business-oriented terms.

An interaction is a system level (external) request of a user (an External Agent, Actor, or another system) and the system or domain that is under analysis. This interaction is often depicted at the context level of the system.

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A popular framework that has become accepted in capturing the details of the interaction is called an operation schema. This non-technical approach provides an easy mechanism to work with customers to fully articulate their requirements. The operation schema assists in documenting the features of a process. One variation of a layout for this best-in-class technique is provided below:
Property Description
Name The name of the interaction. The example above is called "addStock".
Overview A description of the interaction and its purpose.
Reads The information that the interaction reads, e.g. inputs, database tables, etc.
Changes The information that the interaction creates, updates, or deletes, e.g. database tables, transient data (reports), etc.
Preconditions The circumstances (or state of the system) that must be true (assumptions) in order for the interaction to occur or proceed. For instance, a precondition in the example is that a temporal, scheduled, or random event occurred (trigger), the Inventory database is available and the request includes stock, i.e. addStock(stock) - the value of stock is not null.
Scenario The sequence of what occurs in the course of the interaction.
Post Conditions A description of the result(s) of the interaction and the state of the system when the interaction is complete.
Exceptions A list of the possible things that can go wrong.
 
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Last modified: July 14, 2006