Think Different APS 4: Pemodelan Data

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Analisis dan Perancangan

Perangkat Lunak

Quit

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1. PEMODELAN DATA DENGAN

E/R DIAGRAM

The data model also describes the relationship among data

and any constraints that have to be defined on the data.

Data models can broadly be classified into two categories:

Object-based logical model – focuses on describing the

data, the relationship among the data, and any constraints defined.

Record-based logical model – focuses on describing

the data structure and the access techniques in a Database Management System.

A data model is a description of the organization of data in a

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Entity-Relationship Model

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There are various object-based models. The most widely used is the entity-relationship model (E/R model).

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The entity-relationship model is based on a real-world perception that comprises a collection of objects or entities and the relationships among these.

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The diagram used to represent an E/R model is called an E/R diagram.

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The components of an E/R diagram are:

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Entities

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Relationships

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Entities

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An entity is any object, place, person, or activity about which data is recorded.

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Entities are named and represented inside a box.

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There are two types of entities:

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Dependent

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Independent

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Dependent entities are also called weak

entities, and independent entities are called regular entities.

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Relationships

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A relationship is an association among entities.

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A relationship is depicted as a diamond with the name of the relationship type.

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A relationship can associate an entity with itself.

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Multiple relationships can also exist between the same entities.

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There are three types of relationships:

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One-to-One

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One-to-Many

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Attributes

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An attribute is a property of a given entity.

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Attributes are depicted as ellipses, labeled with the name of the property. The key properties are

underlined.

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Weak entity

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A weak entity is an entity whose existence

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Subtypes and Supertypes

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A subtype is a subset of another entity.

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A subtype is always dependent on the supertype for its existence.

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Each entity type (subtype or supertype) maps to a separate table.

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The primary key of the supertype is the

foreign key of the subtype. It creates a link between the two.

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Each entity type (subtype or

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Dua Pendekatan dalam mendesain

Database Relasional

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Pendekatan Top – Down : menggunakan

E/R Diagram

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Pendekatan Bottom – Up : menggunakan

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

Normalisasi dilakukan langkah-demi

langkah, sehingga dari record data yang

kompleks dapat diubah menjadi record

data yang simple.

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Pengulangan-pengulangan data direduksi

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Contoh tabel tanpa proses

normalisasi

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Keuntungan dari proses

Normalisasi



Dengan mereduksi pengulangan data,

maka akan mempercepat proses

pengurutan dan pencarian data.

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Data dengan nilai Null menjadi lebih

minimal sehingga meminimalkan

ketidakkonsistenan data

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Dengan normalisasi, database menjadi

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Normalisasi tahap I

 Setiap sell dari tabel harus memiliki satu nilai data yang

presisi.

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Normalisasi tahap I

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Hasil normalisasi tahap I diperoleh tabel dengan setiap

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Normalisasi tahap II

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Tahap kedua normalisasi dilakukan jika didapatkan

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Normalisasi tahap II

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Dari normalisasi tahap II diperoleh dua buah tabel yaitu

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Normalisasi tahap III

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Normalisasi tahap ini dilakukan jika terdapat beberapa

atribut (bukan atribut kunci) pada suatu tabel dan muncul

berulang –ulang, sehingga memungkinkan untuk

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Normalisasi tahap III

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Atribut Dept dan DeptHead masuk tabel

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Boyce-Codd Normal Form

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Jika pada suatu tabel terdapat lebih dari

satu atribut yang memungkinkan berfungsi

sebagai kata kunci (overlapping candidate

keys), maka candidate keys dapat

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Fourth Normal Form

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If a relation has many-to-many relationships

with two or more relations, then the

attributes of all the three or more relations

cannot be depicted in the same relation.

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When you model such situations in a

relational database, you will either have

redundant data or use null values.

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A condition that requires duplication of

values and thus enforces mutual

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Fourth Normal Form (Contd..)

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You can use fourth normal form (4 NF) to

remove multivalued dependencies.

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A table is in 4 NF if it is in 3 NF and has no

multivalued dependencies.

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To apply 4 NF, you need to put all

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Other Normal Forms

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Some constraints like business rules result in the need for fifth normal form (5 NF).

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For a table to be in 5 NF, it has to be in 4 NF and should abide by some business rules.

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The purpose of 5 NF is to have tables that cannot be further decomposed.

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If the business rule does not exist, then there is no need of 5 NF.

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In addition to 5 NF, there is another normal form called the domain-key normal form (DKNF).

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Other Normal Forms

 Pada tabel berikut untuk departement Computer Science terdapat 3 kode subject yang berbeda : CS150, CS103 dan CS104 yang masing masing diambil oleh 3 student yang berbeda.

 Oleh karena itu departemen ini merupakan domain sehingga kita bisa

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Other Normal Forms

Diperoleh 3 tabel

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Dept – Stud

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Dept – Sub