Level-0 diagram : Project Dictionary entries

For example if you have a "data store" that keeps demographic information, you'd probably keep data like

Name,
Address,
Phone No. etc

in your data store, right?

Then you have to specific in your data dictionary the

"Field Size" of your data fields, i.e. how many characters are you expected to keep the information, e.g., you want to reserve 50 "Characters" for Name, 5 Lines of Address and each line with 50 "Chararcters". You have to specify the Data Size for each column/field in your data store.

Along with the Data Size, you have to advise the "Data Type" too, i.e. if the column/field keeps numeric data only (e.g. Phone No., SSN, etc.), or Alphabetics only (e.g. Name), or Alphanumeric (e.g. Address).

 

Data type is such a basic concept that it is hard to break down.

In a database you have to define the attribute of what is being stored. Let's say you have a table describing students with the fields first_name, last_name, birth_date, age, street address. first_name, last_name, and street address would all be text data types because you are storing strings. birth_date would be a date field. If you're storing the age rounded to the nearest year, you can use a data type of integer/number - no decimals. If you're storing the age rounded to the nearest day (i.e. 22 years and 100 days is 22.274) than you can use a double data type.

For text data types, you have to define how many characters you are going to allow to be stored. So for first_name you may have a field size or length of 20 characters. last_name may be 30. street_address could be 50. Dates and numbers don't have a length, though different number data types will only allow certain ranges of numbers.

Data types vary depending on the type of database you are using.

Make sense?