Question

I have a database (20 tables, up to a maximum of 17 rows) that I need to represent schematically or graphically on one A4 sheet.

I’m looking for a way to do this, since I only know about ER models and I couldn’t manage to squeeze it into a single page.
It could also be a textual representation, as long as it is a standardized way.

Answer 1

Some people call Data Models “ER Diagrams”, which is what you appear to be doing; others call ERDs “Data Models”. Don’t worry about the common usage terms, we have a lot of non-professionals in the industry these days, who call apples oranges. Life is much easier when you use the correct labels.

The Entity Relation Diagram is a schematic of the Entities and Relations (only), that’s why it is called an ER diagram and not a Data Model. Ten tables will easily fit onto an A4 page. You will have space to add notes and text.

The Data Model is the full schematic of the Entities, Relations and Attributes, with the Primary Key differentiated clearly. Depending on the stage of progress and the audience, or the logical vs physical rendering, it will additionally show:

• the other Indices (other than the Primary Key)
• DataTypes
• full detail re the Relations
• Associative tables (many-to-many, shown as a Relation at the Logical level; exposed as a table at the Physical level)

• Subtypes/Supertypes fully exposed

• Depending on whether you use the Relational modelling Standard or not, it will show the subtleties and complexities of the data and its Relations.

• Obviously, if you use Standard notation, then you will be understood by more people, and you never have to go back and change it when more people learn the Standard and expect that notation.

Have a look at the Data Model provided in the link below. The first page is the ERD (28 Entities, while retaining the hierarchy). The DM is delivered in the subsequent 4 x A4 pages, each containing a logical cluster of tables; and all five pages are linked (make sure you find the notes re links, and click on them).

Even for the DM, I find it is best to present information:

• in manageable or understandable chunks, an A4 page containing a logically related cluster,
• which has to be complete it itself (all the parent tables must be shown), which leads to duplication
• but I never duplicate anything
• therefore I define it once, in its natural cluster, and use a collapsed Entity symbol wherever it is referenced, and link the reference to the full definition.

The other technique that I have found that seriously improves understanding, is to show the objects in their natural hierarchy. That technique is detailed in the Notation document.

Another option for you, with only ten tables, is to draw the schema at Data Model level, but only show the Primary Keys (exclude non-PK attributes); one small step beyond ERD, and one big step less than full DM. I do not recommend this, rather, give them the full DM as well as the ERD, on however many A4 pages it takes. People can stop at the first page, or go further if they want.

Link to Example ERD & Data Model

Link to IDEF1X Notation for those who are unfamiliar with the Relational Modelling Standard.