|Lesson 8 || Verbalizing an ER diagram|
|Objective||Describe the process of verbalizing an ER diagram. |
Verbalizing an ER diagram
Once an ER diagram is completed and especially if the diagram is huge, as is often the case with a database containing a dozen or more tables, many designers will opt to verbalize the diagram for quick reference and to provide a second source of documentation.
The ER diagram for Stories on CD is translated into relational notation this way, with entity names followed by attributes enclosed in parentheses. Note that the entity name is now plural, reflecting the name you will ultimately give to the table in the database itself.
Customers (CustID PK, CustLast, CustFirst, CustStreet, CustCity, CustState,
CustZip, CustPhone) Orders (OrderNo PK, CustID FK, OrderDate)
Line Items (OrderNo CPK/FK, CDNo CPK/FK, Quantity,
SellingPrice, LineCost, Shipped)
CDs (CDNo PK, CDTitle, DistID FK, RetailPrice, AgeGroup, Description)
Distributors (DistID PK, DistName, DistStreet, DistCity, DistState, DistZip, DistPhone)
The relational notations retain the information necessary to translate them into basic database tables. However, unlike an ER diagram, this type of notation is not a particularly good tool for communicating the structure of a database to end users. It is principally for the benefit of the database designer, and often comes in handy when standardizing on names
for entities(tables) and attributes(fields).
As with an ER diagram, there is no “standardized” notation for verbalizing a diagram; consistency is the only rule of thumb. The next lesson concludes the module.