[thelist] ERD tool

martin.p.burns at uk.pwcglobal.com martin.p.burns at uk.pwcglobal.com
Wed Apr 3 00:56:01 CST 2002

Memo from Martin P Burns of PricewaterhouseCoopers

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Subject:    Re: [thelist] ERD tool

>> What differentiates it from UML?

>what differentiates ERD from UML?

>entity-relationship diagramming is a technique for drawing the entities
>the relationships between entities in a database

Whereas UML is used for a much wider range of documentation than the
db design. With UML you can define how the *entire* system works, not
just the db. For db work, then, UML is overkill... (although a lot of UML
also be napkin sketched but for a complex system you'll need a big napkin).

as you say:

>to be fair, though, ER diagramming looks only at the structure of the
>stored data, whereas UML covers everything-- business rules, interface
>design, code module structure, use case, et cetera

>the following remark may come across as cynical, but i suspect you need
>some bigass tools to produce (dare i say understand) UML designs -- the
>spec itself is a 10 megabyte PDF

The specs are complex, but you don't need complex tools as much as a
switched on brain - if you're doing UML in any depth, you're probably
a complex system.

Actually, you don't need to use the full spec to be useful. Even a complex
like Zope only uses one of the the most basic elements of UML - the Use

The broad outlines of the project captured in the Vision Statement are then
fleshed out in Use Cases. The Fishbowl Process focuses on a pragmatic,
simple approach: do as little as possible while still achieving the main
goal of truly understanding the requirements of the project. Use Cases in
the Fishbowl are not meticulously specified with fifteen fields or so as in
other processes. A Use Case in the Fishbowl must at least:

State the goal from point of view of the user

Name the actor (kind of user) performing the use case

Provide enough descriptive text to ensure that you've thought things

A good way to handle the description is to write it in a user documentation
style as if it were to be consumed by the actor. This will often give you a
head start on user documentation :^)

If you've used Use Cases in an organization before then you know that there
are endless opinions on how they should be done. The main goal is that they
provide a common understanding of the requirements. Community review is the
best way to make sure that this goal is achieved. A good way to get started
with Use Cases is to find a project fairly similar to your own and use the
way that that project's use cases were done as a guide for your own.

>> And yes, Visio does what you are asking for.
>does it produce the DDL (the "create table" statements) from the diagram?
>neat, but, being a microsoft product, does it produce DDL for any
>other than sql/server and access?

I think what it does is the next step - actually create the db with empty
tables. But
I think you're right, it's MS products (possibly even access) only.


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