conceptual model
the logical structure of the entire database
Based on the needs of various departments, the conceptual model is the first model created.
conceptual schema
another term for logical schema
Adding or removing entities, attributes or relationships in the conceptual schema should be possible without changing existing external schemas.
data independence
the immunity of user applications to changes made in the definition and organization of data
Data independence refers to the immunity of user applications to changes made in the definition and organization of data.
data model
a collection of concepts or notations for describing data, data relationships, data semantics and data constraints
In the second step, the data items, the relationships and the constraints are all expressed using the concepts provided by the high-level data model.
data modelling
the first step in the process of database design
Data modelling is the first step in the process of database design.
database logical design
defines a database in a data model of a specific database management system
Database logical design defines a database in a data model of a specific DBMS.
database physical design
defines the internal database storage structure, file organization or indexing techniques
Database physical design defines the internal database storage structure, file organization or indexing techniques.
entity relationship diagram (ERD)
a data model describing the database showing tables, attributes and relationships
A schema is an overall description of a database, and it is usually represented by the entity relationship diagram (ERD).
external model
represents the user’s view of the database
Let’s look at this from the highest level, the external model.
external schema
user view
The ability to change the logical schema, without changing the external schema or user view, is called logical data independence.
internal model
a representation of the database as seen by the DBMS
Physical data independence refers to the immunity of the internal model to changes in the physical model.
logical data independence
the ability to change the logical schema without changing the external schema
The ability to change the logical schema, without changing the external schema or user view, is called logical data independence.
logical design
where you create all the tables, constraints, keys, rules, etc.
This is often referred to as the logical design.
logical schema
a conceptual design of the database done on paper or a whiteboard, much like architectural drawings for a house
A logical schema is a conceptual design of the database done on paper or a whiteboard, much like architectural drawings for a house.
operating system (OS)
manages the physical level of the physical model
The physical level of the database is managed by the operating system (OS).
physical data independence
the immunity of the internal model to changes in the physical model
Physical data independence refers to the immunity of the internal model to changes in the physical model.
physical model
the physical representation of the database
The physical model is simply the way the data is stored on disk.
schema
an overall description of a database
A schema is an overall description of a database, and it is usually represented by the entity relationship diagram (ERD).
hierarchical model
represents data as a hierarchical tree structure
The hierarchical model represents data as a hierarchical tree structure.
instance
a record within a table
Each record is said to be an instance of the membership table.
network model
represents data as record types
The network model represents data as record types.
relation
another term for table
The relational model represents data as relations, or tables.
relational model
represents data as relations or tables
The relational model represents data as relations, or tables.
set type
a limited type of one to many relationship
This model also represents a limited type of one to many relationship called a set type, as shown in Figure 4.1.
These terms were extracted from Database Design – 2nd Edition by Adrienne Watt, eCampusOntario (originally published by BCcampus) which is licensed under a Creative Commons Attribution 4.0 International License. Chapter text adapted from Database System Concepts by Nguyen Kim Anh, licensed under CC BY 3.0.