Entity Relationship Diagrams or ERDs
1. Why we need it?
They help us to visualize how data is connected in a general way and are particulary useful for constructing a relational database.
2.What is it?
Entity Relationship Diagrams or ERDs is a logical structure of database. ERDs shows the relationship of entity sets stored in a database. An entity in this context is a component of data. In other words, ERDs illustrate the logical structure of databases.
3.How to use it?
It has some different types. For example Information Engineering style, Chen style, Bachman style, Martin style, etc.
The below picture is combine Information Engineering style and Chen style.
-Components and ERDs Cardinality
-Entities : Which are represented by rectangles. An entity is an object or concept about which you want to store information.
-Actions/ Relationship : Which are represented by diamond shapes show how two entities share information in the data base
-Attributes : Which are represented by ovals, A key attribute is the unique distinguishing characteristic of the identity.
-Primary key : Which is an attribute that uniquely identifies every record in a certain table. And since a single attribute can accomplish all that, it makes sense that you will need just one primary key per entity.
-Lines : Cardinality specifies the maximum number of relationships and ordinality specifies the maximum number of relationships and ordinality specifies the absolute minimum number of relationships.
4.In our case
The data is from “Table 1. Health expenditure by function in 2000–2017, current prices, € million”