Here we will introduce an example using Dcase description steps.In DEOS an annual demo is held at ET(Embedded Technology Exhibition in Japan).
Fig.6 illustrates a web server system which was demonstrated in 2011.Let`s write a Dcase for this system.Here we will use a description experiment conducted by the DEOS center.
1.Define the system life cycle, summarize input-output document of each phase
This web server system was developed by integrating existing server PCs.Fig.7 illustrates its life cycle and input, output documents.However, since it is a demo system there is a possibility that some of the documents do not actually exist.Here we will focus on the operational work-flow definition document.
2.Categorize input, output documents
Input, Output document of each phase is organised and categorized from the dependability viewpoint.This becomes an input when writing a D-case.
3.State a top goal : “the system is dependable”
The top goal of Dcase is a claim that relates to dependability of a system.First we put the sentence "the system is dependable".Then, change and elaborate according to the targeted system.In this example we assumed, "the web server system sufficiently satisfies the SLA (Service Level Agreement)".
4. Top goals are established in the context of dependability requirements, environment information and definitions.
Dependability requirements, environment information and definitions are established as top goals to further clarify the scope of the system.In the following example SLA(Service Level Agreement) are equivalent to dependability requirements.
5. Grasp the structure of the D-Case
It is tedious work to devide top goals into corresponding sub-goals.So we recommend that you a grasp the structure of the D-Case and then argue accordingly.Fig.9 illustrates the structure of a D-Case roughly and we can use this to strengthen our discussions.
6. Required documents are established as contexts.
We require documents that explain the workflow if we are to discuss the operations workflow in detail.
7. Create a D-Case subtree from documents
We can use the structure of a document to automatically define and expand top goals into subgoals.In the following example (Fig.10) the D-Case top goals are exapanded according to the steps in the workflow document.(Note: only the first and the last step is expanded)