Data Model, Database Schema and Instant
Data models can be grouped based on the concept of making a database structure description, namely:
1. The conceptual data model (high level) presents concepts about how users perceive or treat data. In this model, three concepts of data presentation are introduced, namely:
Entity (entity) is the presentation of objects, events or real-world concepts whose existence is explicitly defined and stored in a database, for example: Students, Subjects, Lecturers, Values and so forth.
Attributes are information that explains the characteristics of an entity such as Name, Faculty, Department for Student entities.
Relationship (relationship) is a relationship or interaction between one entity with another, for example a customer entity related to the entity of goods purchased.
2. Fiscal data model (low level) is a concept of how detailed description of data is stored into a computer by presenting information about the recording format, the order of the recording, and data access paths that can make searching for data records more efficient.
3. Implementation data model (representational) is the concept of description of data stored in a computer by hiding part of the detailed description of the data so that users get a global picture of how the data is stored on the computer. This model is a data model concept used by the hierarchical, network and relational models.
Database Schema and Instant
Database schema is a description of the database whose specifications are determined in the design stage but are not expected to be changed at any time. Schematic depictions generally only contain a part of the database description description.
Database Schema and Instant
A group of data that is arranged in a row of records (record / tuple) and stored in a database is called instances or occurences.
Relational Data Model
In the relational model, the database will be "spread" or sorted into various two-dimensional tables. Each table always consists of a horizontal row called a row of data (row / record) and a vertical row commonly referred to as a column (column / field).
Example of a Table and its connectedness:
Relational Data Model
Advantages of Relational Database
The shape is simple
Easily perform various data operations
Terms in the Relational Database:
Relation
A relation is a table consisting of several columns and several rows. Relationship shows the relationship between a number of entities originating from a set of different entities. Entities are individuals who represent something tangible and can be distinguished from the others.
Attribute
Attributes are columns in a relation. Each entity must have an aribut that describes the character of the entity. Determination or selection of attributes that are relevant to an entity is important in the formation of data models.
Tuple
Tuple is a line in a relation or a collection of interconnected elements that inform about an entity in full. One record represents one data or information about a person, for example: NPM, student name, address, city, etc.
Domain
A valid set of values for one or more attributes
Degree
The number of attributes in a relation
Cardinality
The number of tuples in a relation
Graph attribute
Relational Key
Super key
An attribute / set of attributes that uniquely identifies a tuple in a relation.
Candidate key
An attribute or a minimum set of attributes that uniquely identifies a specific event of an entity. An attribute in a relation that usually has a unique value. A minimum set of attributes implies that we cannot remove several attributes in the set without destroying unique ownership.
Primary key
Is an attribute or a minimum set of attributes that not only uniquely identifies a specific event, but can also represent each event of an entity. Candidate key chosen to uniquely identify a tuple in a relation. Each candidate key has the opportunity to become a primary key, but it is better to choose one that can represent the whole entity.
Alternate key
Is a candidate key that is not used as a primary key or Candidate key that is not selected as a primary key.
Foreign key
Attributes with the same domain that are the primary key in a relation but in other relations these attributes are only as ordinary attributes. The guest key is placed on a subsidiary entity and is the same as the primary primary key associated.
Relational Key
Relational Integrity Rules
Null
The value of an attribute that is unknown and is not suitable for that line (tuple). Null value (constant) is used to declare / fill in attributes whose value is indeed not ready / missing.
Entity Integrity
There is no one primary key component that is null.
Referential Integrity
A domain can be used as a primary key if it is a single attribute on the domain in question. Languages in Relational Databases Use query language statements submitted to retrieve information. Query Language (Query Language) is more emphasized on the aspect of searching data from within a table. This search aspect is so important because it is the core of the effort for data management.
Database Creation
In making a database there are several stages, including:
Collection and Analysis
Define user groups and their application fields: identify application fields and user groups, then select user group members who can be used as the main user keys that can represent their groups
Review existing documentation: study and analyze the documents in a particular application.
Analysis of the operating environment and data processing: studying the system that is running either still using the human system or already using a computer system
Questionnaire and interview: to potential users who are deemed potential to obtain the required information and process specifications.
Conceptual database design
Conceptual scheme design: about the organization of data that must be stored in a database
Transaction design: conducted to obtain information from the database system analysis results in stage 1
Database design process
Collection and analysis of requirements
Conceptual database design
Selection of DBMS
Mapping from conceptual to logical
Physical Design
Implementation