ERM- Entity-Relationship model a systematic data model that describes the data or information aspects within a domain or the process of data. This data can be visualised in the form of retaliative data via a mindmap/branch. Components of ERM include such things as entities which are the relations that exist within a domain and all divided under compartments. Such programmes like MySQL & Myadmin follow this through their data base.
Breakdown of ERM example:
Entities- link inter-link each other through the relationships that show the colony and the requirements between them, e.g. a room can be divided into zero or more sections, but there can only be one section in a room. The entities (foreign keys) can have individual attributes which characterises them. Diagrams are created to show this relationship.
ERD/ERM in reference to money printers:
- Money printer contributors can store personal data
- Each money printer have the option to produce 1 or more notes
- Each note has the name of the money, who produced it and what it is worth ( description)
- Each note has at least one or many important people on the note
- Each important on the note has its own description
Three levels of ERM models:
Conceptual data: Known to be the highest ERM model, accommodates the least amount of data but organises the backbone of a model. Conceptual data is defied as the master reference of data within a organisation.
Logical data: Logical data doesn’t require data from the Conceptual as it only consists of developing and only necessary information, this is because logical data contains more detail. This gives the characteristics of the data.
Physical data: Physical data can be produced from each logical model section, as it is developed to be recognised as a database. In this case, each physical model should have the right amount of detail to create a database.
Here are examples of ERM:
Three-tier architecture using Lamp:
HTML -> request -> PHP -> request -> Mysql
HTML <- response <- PHP <- response <- Mysql
Presentational tier-Presentation tier(Gui)-Acess via Client
Middle tier-(business logic)-}Server
Data tier (data persistence)-}Server
ERD/ERM in form of a game