database and entity relationship diagram

April 19, 2009 at 1:58 am (Tidak terkategori)

database and entity relationship diagram

the definition of database
* collection of data which stored in magnetic disk, optical disk or other secondary storage
* collection of data which is linked one to other of an enterprise.(factory, govermental institution, or private section)
* manufactur company -> production planning data, actual production data, data ordering material
* hospital -> data of patient, doctor, nurse, etc

database management system
* collection a database with software application in based of database
* this software application is use for accessing and maintaining the database
* the first aim of DBMS is to preparing an easy and efficient environment for using, collecting, and storing data and information

bit, byte, field
* bit : is the smaller part of data, which contain of value 1 or 0
* byte : collection of same kind of bit
* filed : collection of same kind of byte, which in database is called “attribute”

types of attribute

– single vs multivalue

  • single -> only can containing mostly 1 value
  • multivalue -> can containing more than 1 value with same kind value

– atomic vs composition

  • atomic -> cannot divided into smaller attribute
  • composition -> alliance of smaller attribute

– derived attribute -> attribute that can be yield from other attribute value, for example : age can be yield from attribute of birth datenull

– value attribute -> attribute with no value for a record

– mandatory value attribute -> attribute that must have a value
record or tupple
– a data row inside a relation
– consist of attribute collection which attribute interaction for advising entity or relation as detail
entiry or file
file is collection of record that have same kind and same element, which the same attribute, but different data value.
– Type of file
In application process, file can be categorized as :

  • Main file
  • Transaction file
  • Report file
  • History file
  • Protector file
  • Activity file

Domain

collection of value that can be inside one or more attribute.

– Each attribute in database relation defined as domain.

Element key of data

Key is element of record that used for finding its in access time or can be used for identification each entity/record/row.

types of attribute

– single vs multivalue

  • single -> only can containing mostly 1 value
  • multivalue -> can containing more than 1 value with same kind value

– atomic vs composition

  • atomic -> cannot divided into smaller attribute
  • composition -> alliance of smaller attribute

– derived attribute -> attribute that can be yield from other attribute value, for example : age can be yield from attribute of birth datenull

– value attribute -> attribute with no value for a record

– mandatory value attribute -> attribute that must have a value
record or tupple
– a data row inside a relation
– consist of attribute collection which attribute interaction for advising entity or relation as detail
entiry or file
file is collection of record that have same kind and same element, which the same attribute, but different data value.
– Type of file
In application process, file can be categorized as :

  • Main file
  • Transaction file
  • Report file
  • History file
  • Protector file
  • Activity file

Domain

collection of value that can be inside one or more attribute.

– Each attribute in database relation defined as domain.

Element key of data

Key is element of record that used for finding its in access time or can be used for identification each entity/record/row.

SPECIES OF KEY
There are several types of key in the ERD, namely:

  • Superkey is one or more attributes of a table that can be used to identify entityty / record of the table are unique (not all attributes can be superkey)
  • 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 superkey 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 criteria, namely:

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

  • Alternate Key is the 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 cardinality one to many or 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.
Differences between the DFD and ERD, namely:

1. DFD is a model of network functions that will be implemented by the system.
2. ERD is a model that emphasizes the network data on the structure and relationship data.

element in 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.

* relationship
In the ER diagram, the relationship can be described with a rhomb. 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 which participating in a relationship. Degree is unit which is often used in the ERD.

* attribute
Attribute is the nature or characteristics of each entity and relationship

* cardinality
Cardinality indicates the maximum number of record/tuple that can be relation with the entity on the other entity

degree of relationship
* Unary relationship
is the relationship model between the entity originating from the same entity set.
* binary relationship
is the relationship model between 2 entities
* ternary relationship
is a relationship between the instance of 3 types of entities are unilateral

cardinality
* 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.

example:
1

* 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 have to seen.For an incident on the first entity can have many relationships with the incident on the second entity, if the one incident in which two entities can only have a relationship with one incident on the first entity.

example:
21

* many to many
if any incident occurs in an entity has many relationships with other entities in the incident.

example:
31
Notation (E-R diagram)

Symbolic notation in the ER diagram, namely:

1. Rectangle represent the collective entity
2. Circle represent the attributes
3. Rhomb represent collective relationships
4. Line as the set of relationships between the entity and the collective entity with the attribute

41

Reference:

  1. ER Ngurah Agus Sanjaya. Slide Part 5 – DATABASE DAN ER-DIAGRAM.
  2. Elmasri & Navathe, Fundamental of Database Systems, 5th Edition, Chapter 3, 2007.

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