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Database and ERD (Entity Relationship Diagram)
definition of database
Some definitions from the Database in a number of perspectives:
• collective group data (records) that are organized each other in such a way that can later be used again quickly and easily.
• Collection of interrelated data stored together in such a way, and without repetition (redundancy) is not necessary, to meet various needs.
• Collection file / table / the related stored in electronic storage media.
• a set of data stored in the magnetic disk, optical disk or other secondary storage. Collection of integrated data-related data of an enterprise (company, government or private)
Example:
Manufacturing companies have production planning data, actual production data, data ordering materials, etc.
Hospitals have patient data, doctor, nurse, etc.
University faculty have the data, faculty, students, staff, etc.
DBMS (Database Management System)
DBMS software is designed to assist in the maintenance and
utility data collection in large numbers. DBMS can be the alternative
specifically to the use of applications, such as storing data in files and
write code for a specific application settings.
Benefits of Using DBMS
DMBS use to manage data have several advantages, namely:
Freedom of access to data and efficient
• reduction time application development
• integrity and data security
• Administrative uniformity data
• simultaneously access and improvements to the occurrence of crashes (crash of simultaneous process).
definition of bit, byte, and field
Data bit is the part that contains the smallest value of 0 or 1
Bytes-bit set of bit similar
Field set of byte-byte similar, in the database used the term attribute
Attribute / Field
It is the nature or characteristics of an entity that provides provide detail on these entities. within a relationship can also have attributes
Example attributes:
Lecturer: NIP, NAME, ADDRESS
STUDENTS: NIM, NAME, ADDRESS
CAR: NOMOR_PLAT, COLOR, TYPE, CC
Types of attributes
Single vs. multivalue
In the single type can only be filled at most only one nila
In the multivalue types 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
The composition is a combination of several attributes of a smaller
Derived attribute
attribute value can be derived from the value of other attributes, such as age attributes resulting from the date of birth attribute
Null Value attribute
Attributes that have no value to a record
Mandatory attribute Value
Attribute must have a value, usually this is a primary key in an entity
RECORD / TUPLE
It is a line of data in a relationship, and consists of a set of attributes where the attribute-attribute-attribute is to inform each other entity / relationship fully
In the picture above is an example record NIM 9455500001, the name of Abdullah, the address of the feast, no4, this is a record
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 category as follows:
- Master File
- Transaction Files
- File Reports
- File History
- File Protection
- File Work
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
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.
The types 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)
Cadidate Key is a super key with minimal attributes. 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 guaranteed the unique
Alternate Key is an attribute of the 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 cardinal 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.
Entity Relationship Diagram
ERD is a model of a network that uses word order is stored in the abstract system.
Differences between the DFD and ERD
DFD is a model of network functions that will be implemented by the system and the flow of data from the program
ERD is a model that emphasizes the network data on the structure and relationship data. ERD will be visible in the clear relationship between the data with other data.
The elements of ERD
Entity
In the ER Diagram Entity is described with the form of a rectangle. Entity is something that exists in the real system and the abstract where the data stored or where there are data.
Example
Individuals : employees, customers, students, distributor.
Place: room, building, office, field, campus.
Object: books, motorcycles, software packages, products
event: registration, reservation, billing
Concept: bank account, and qualification.
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 relation.
Relationship Degree
is the number of entities participating in a relationship. Degree which is often used in the ERD.
Attribute
It is the nature or characteristics of an entity that provides provide detail on these entities. within a relationship can also have attributes
Example
Customer Attributes
No KTP / SIM
Name
Address
Cardinal
Figures show that the appearance of a large number of objects associated with the occurrence of the object on a relationship, a combination that may: (1:1, 1: N, M: N)
There are 3 relations cardinal, namely
- 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 seen . for an incident on the first entity can have any relationship with much incident on the second entity, if the one incident on the second entity can only have one relationship with the incident on the first entity.
- Many To Many: if any incident occurs in an entity much have relationships with other entities in the incident.
- Unary Relationship
model is the relationship between the entity originating from the same entity set.
- Binary Relationship
model is the relationship between 2 entities.
- Ternary Relationship
is a relationship between the instance of 3 types of entities are unilateral.
Symbolic notation in the ER diagram is
Rectangle represent the collective entity
Circle represent the attributes
rhomb state collective relationships
Line as the set of relationships between the entity and the collective entity with attribute collective
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