Chapter No 2
ERD (Entity Relation Diagram)
2.1 History of ERD
An entity-relationship model (ERM) is an abstract and conceptual representation of data. Entity-relationship modeling is a database modeling method, used to produce a type of conceptual schema or semantic data model of a system, often a relational database, and its requirements in a top-down fashion. Diagrams created by this process are called entity-relationship diagrams, ER diagrams, or ERDs.
This technique was developed by PETER CHEN in 1976 since …show more content…
A table in Access is quite different then a table in real life. Instead of having wooden legs and being used for meals, Access Tables are a grid made up of rows and columns. Here's an example of a table in Access:
There are for key components we want you to learn right now: 1. tbl_Sales: The name of our table is the example is "tbl_Sales". Note that we could have simply called our sales table Sales, but by including a prefix tbl_ there is absolutely no confusion and is a great Access habit to pick up! 2. Columns: A column is one vertical section of the table (i.e. up-and-down sections). The vertical columns have their label at the top and these labels should describe the type of information that will be stored. The columns in this table are: Employee, Product, Price and Sale Number. 3. Rows: A row is one horizontal segment of the table (i.e. left-to-right sections). One record takes up exactly one row. For example, in this table one