Database And ER-Diagram

DATABASE DEFINITION
Database is a set of data which is stored on a magnetic disk, disk optics or other secondary storage. Can also mean the collection of data linked to something other than a company. (factory, governmental institution, or part time)

• Manufacture company for example production planning data, real data, the order data
• hospital data e.g hospital data from patients, doctors, nurses, etc..

DATABASE MANAGEMENT SYSTEM
Database Management System is a collection of databases with software applications based database. Program applications are used to maintain the database. The main purpose DBMS is to prepare an environment for efficient and easy to use, collection, and store data and information.

BIT, BYTE, Field

• Bit is the smallest of the data containing the values 1 and 0.
• Byte is a set of bit-a bit similar.
• Field is a set of byte-byte similar, in the database used the term attribute.

Attribute / Field
It is the nature or characteristics of an entity which provides the-provide detail on these entities. A relationship can also have attributes. Example attributes are:
STUDENTS: ID, NAME, ADDRESS
CAR: SIGN_NUMBER, COLOR, TYPE, CC

TYPES of Attribute
Single vs. multivalue
Single, can only be filled at most one value
Multivalue, can be filled with more than one value with the same type of

Atomic Vs. composition
Atomic, can not be divided into the attributes of smaller
Composition, a combination of several attributes of a smaller

Derived attribute
Derived attribute is an attribute whose value can be derived from the value of other attributes, e.g age generated from the date of birth attribute

Null Value attribute
Null Value attribute is an attribute that has no value to a record

Mandatory attribute Value
Mandatory Value attribute is an attribute that must have a value.

RECORD / TUPLE
Record / tuple is a row of data in a relationship that consists of a set of attributes where the attribute-attribute-attribute is to inform each other entity / relationship fully.

Entity / FILE
File is a collection of similar records and have the same elements, the same attributes but different data value.

File Type
In processing applications, files can categorized as follows:

• Master File
• File Transactions
• File Reports
• File History
• File Protection
• The Job

DOMAIN
Domain is the set of values that are allowed to reside in one or more attributes. Each attribute in a database relational is defined as a domain.

Element KEY DATA
Key elements of record which is used to find these records at the time of access, or can also be used to identify each entity / record / line.

SPECIES OF KEY
Super Key is one or more attributes of a table that can be used to identify entity / record of the table are unique (not all attributes can be super key)

Candidate key is super key attributes with minimal. Candidate must not contain a key attribute of the table so that the other candidate key is certain super key but not necessarily vice versa.

Primary Key. One of the key attributes of the candidate can be selected / specified a primary key with the three following criteria:

1. Key is more natural to use as reference
2. Key is more simple
3. Key is unique guaranteed

Alternate Key attributes of a candidate key is not selected to be primary key.

Foreign key is any attribute that points to the primary key in another table. Foreign key will be going on a relationship that has cardinality one to many (one to many) or many to many (many to many). Foreign key is usually always put on the table that point to many.

External Key is a lexical attribute (or set of lexical attributes) that values are always identify an object instance.

ERD (Entity Relationship Diagram)
ERD is a model of a network that uses word order is stored in the abstract system. There are the different between ERD and DFD, among others, DFD is a model of network functions that will be implemented by the system while, ERD is a model of network data that emphasizes the structure and relationship data.

Elements of the ERD

Entity
In the ER diagram represented entity with rectangular shape. Entity is something that is in real or abstract system where data is saved or where data is available.

Relationship
ER diagram on the relationship can be described with a lozenge. Relationship is a natural relationship that occurs between entities. In general, the name given to the verb base making it easier to do the reading the relation.

Relationship Degree
Relationship Degree is the number of entities participating in a relationship. Degree which is often used in the ERD.

Attribute
is the nature or characteristics of each entity and relationship.

Cardinality
Cardinality is how tupel maximum amount that can be related with entities on the other entity

Relationship Degree
Unary Relationship
Unary Relationship model is the relationship between the entity originating from the same entity set.
Binary Relationship
Binary Relationship model is a relationship between 2 entities.
Ternary Relationship
Ternary Relationship is a relationship between the instance of 3 types of entities are unilateral.

CARDINALITY
There are 3 cardinalities relations in the

• One to One: Level one to one relationship with the one stated in the entity’s first event, only had one relationship with one incident in which the two entities and vice versa.

• One to Many or Many to One: Level one to many relationship is the same as the one to many depending on the direction from which the relationship looked. For an incident on the first entity can have any relationship with many incident on the second entity, if the one incident on the the second entity can only have one relation with the incident on the first entity.

• Many To Many: if any incident occurs in an entity banyaj have relationships with other entities in the incident.