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5/29/2008 2:36 AM

	adrian
446 posts

Re: Context Diagram: Bank ATM Example

Hi Guys,

Here's some feedback/answers related to your questions and Level 1 diagrams (not necessarily in same order):

Yes - requirements elicitation is an ongoing process! There is no such thing as perfect process, model, system, etc. The more you are familiar with a system and the given business domain the more you will uncover new requirements and areas which should be refined. Requirements gathering is an iterative process. This is why prioritization should be a key concept for every business analyst. The BA should prioritize at every step in the process; for example at the problem statement state consider which are the most pressing business needs, at vision level consider which features are most important, at the requirements level identify the high priority requirements, at the data flow modeling level identify the key processes. So at every step work first on the most important things first and then move to the next step of the process (you can refine later) or else you'll never go anywhere.
Sonavi: related to the item above - in the Level 1 diagram you need to show the key processes (Withdraw Cash, Deposit Money, etc.) your diagram has none of those. Things like "Display Error Message" are too detailed at this level and not very important at this time. Same goes for: "Display Options", "Exit Session", "Send for data input and outputs
Data flows from Entities must flow into Processes
Data flows to Entities must come from Processes
Processes and Data Stores must have both inputs and outputs; what goes in must come out!
Inputs to Data Stores only come from Processes
Outputs from Data Stores only go to Processes

A few more corollaries:

There can be no Data Flows between Entities
There can be no Data Flows between Data Stores
There can be no Data Flows between an Entity and a Data Store

- Adrian

Adrian Marchis
Publisher - ModernAnalyst.com
Random Thoughts of an Analysis Manager

5/29/2008 9:17 AM

	ajmarkos
86 posts

Re: Context Diagram: Bank ATM Example

Adrian:

Data Flow Diagrams or Use Cases?

It has always been my experience that , especially for larger scale efforts, proceeding in a pure top-down fashion (i.e., STARTING with a Context diagram that is anywhere near adequate and then proceeding to lower level diagrams) is not possible. If an analyst is on a larger scale project where someone, anyone, has, at the start fo the project, an adequate top-down understanding of the essential functionality within the scope of the system, I would say that analyst is in a very rare situation. Recognizing this unfortunate but typical reality is key, as it helps explain why good Context diagrams, especially for larger scale efforts, are so rare in the business world.

It has always been my experience that the analyst(s) need to proceed from somewhere in the middle and then go up levels of abstraction. In other words, we must first create some lower level data flow diagrams and then summarize them upwards into a Context diagram.. I know, if we could start from a context diagram, analysis would be alot easier.

At what point can we switch to use cases? That point is debatable. However, for larger scale projects, the required need for data flow diagrams often extends well beyond the Context diagram.

Tony

5/29/2008 3:15 PM

	adrian
446 posts

Re: Context Diagram: Bank ATM Example

Hi Tony,

I would argue that it is up to the Business Analyst to ensure that they have all they need in order to start with a top-down approach. Every project should have some sort of charter and problem statement or list of needed features. I realize that the business analysis process is an iterative one and that not all info gets discovered upfront. As new info is discovered the models should be updated.

- Adrian

Adrian Marchis
Publisher - ModernAnalyst.com
Random Thoughts of an Analysis Manager

6/1/2008 10:55 PM

	Jay
10 posts

Re: Context Diagram: Bank ATM Example

Hello Adrian and team members

Thanks for the reply and the feedback. I have gone ahead and modified the diagrams . I have tried to keep in mind the data flow rules. I have given both the level 1 diagram and the level 2 diagrams. Adrain, would be great if you can tell me whether I am going in the right direction and where I am going wrong. Once this is done, I would like to go ahead and create use case diagrams .

Would like other team members to participate and give their views and opinions and guide us where we are going wrong.

Thanks :- Jay