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Analisis dan Perancangan Perangkat Lunak

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PEMODELAN DATA

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Konsep Pemodelan Data

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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 database.

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Entity-Relationship Model• There are various object-based models. The most

widely used is the entity-relationship model (E/R model).

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

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

• The components of an E/R diagram are:• Entities• Relationships• Attributes

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Entities• An entity is any object, place, person, or

activity about which data is recorded.• Entities are named and represented inside a

box.• There are two types of entities:

• Dependent• Independent

• Dependent entities are also called weak entities, and independent entities are called regular entities.

• Weak entities are represented by double-lined boxes.

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Relationships• A relationship is an association among entities.• A relationship is depicted as a diamond with

the name of the relationship type.• A relationship can associate an entity with

itself.• Multiple relationships can also exist between

the same entities.• There are three types of relationships:

• One-to-One• One-to-Many• Many-to-Many

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Attributes• An attribute is a property of a given entity.• Attributes are depicted as ellipses, labeled with the

name of the property. The key properties are underlined.

• A relationship can also have attributes.

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One-to-One Relationship

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One-to-Many Relationship

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Many-to-Many Relationship

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Weak entityA weak entity is an entity whose existence

depends on some otherentity.

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Subtypes and Supertypes

Subtypes and Supertypes • A subtype is a subset of another entity.• A subtype is always dependent on the

supertype for its existence.• Each entity type (subtype or supertype) maps

to a separate table.• The primary key of the supertype is the

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

• The foreign key of the subtype is also its primary key.

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Subtypes and Supertypes

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

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If there are any entities with common attributes, merge the entities.

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Attributes may Become Entities

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Specialization

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Generalization

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The previous E/R diagram can be converted using aggregation

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The previous E/R diagram can be converted using aggregation

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2. Normalisasi dan Denormalisasi Data

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Dua Pendekatan dalam mendesain Database Relasional

Pendekatan Top – Down : menggunakan E/R Diagram

Pendekatan Bottom – Up : menggunakan proses Normalisasi dan denormalisasi

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Normalisasi dilakukan langkah-demi langkah, sehingga dari record data yang kompleks dapat diubah menjadi record data yang simple.

Pengulangan-pengulangan data direduksi tanpa menghilangkan informasi yang diinginkan.

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Contoh tabel tanpa proses normalisasi

Pada tabel tersebut, Student ID, Student Name muncul lebih dari sekali dengan nilai yang sama. Namun demikian ada antribut lain yang ikut diulang : StudentAddress, StudentBirthdate, StudentCity, StudentZip, yang merupakan pengulangan data yang tidak perlu.

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Keuntungan dari proses Normalisasi

Dengan mereduksi pengulangan data, maka akan mempercepat proses pengurutan dan pencarian data.

Data dengan nilai Null menjadi lebih minimal sehingga meminimalkan ketidakkonsistenan data

Dengan normalisasi, database menjadi lebih compact

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Normalisasi tahap I Setiap sell dari tabel harus memiliki satu nilai data yang

presisi. Pada berikut kolom Hours berisi data lebih dari satu

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Normalisasi tahap I Hasil normalisasi tahap I diperoleh tabel dengan setiap

sell hanya berisi satu nilai, walaupun akhirnya terdapat pengulangan data pada kolom tertentu

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Normalisasi tahap II Tahap kedua normalisasi dilakukan jika didapatkan

beberapa atribut berulang, sehingga memungkinkan beberapa atribut tadi dipecah pada tabel berbeda

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Normalisasi tahap II Dari normalisasi tahap II diperoleh dua buah tabel yaitu

tabel EmployeeDept dan tabel Project

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Normalisasi tahap III Normalisasi tahap ini dilakukan jika terdapat beberapa

atribut (bukan atribut kunci) pada suatu tabel dan muncul berulang –ulang, sehingga memungkinkan untuk dipecah pada tabel berbeda.

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Normalisasi tahap IIIAtribut Dept dan DeptHead masuk tabel

baru dengan nama Departement

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Boyce-Codd Normal FormJika pada suatu tabel terdapat lebih dari

satu atribut yang memungkinkan berfungsi sebagai kata kunci (overlapping candidate keys), maka candidate keys dapat dipecah pada tabel yang berbeda

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Fourth Normal Form

• 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.

• When you model such situations in a relational database, you will either have redundant data or use null values.

• A condition that requires duplication of values and thus enforces mutual independence of multivalued attributes is called multivalued dependency.

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Fourth Normal Form (Contd..)

• You can use fourth normal form (4 NF) to remove multivalued dependencies.

• A table is in 4 NF if it is in 3 NF and has no multivalued dependencies.

• To apply 4 NF, you need to put all multivalued attributes in individual tables containing the key to which the attribute values apply.

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Fourth Normal Form

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Fourth Normal FormHasil Normalisasi ke 4

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Other Normal Forms

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

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

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

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

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

• A table is in DKNF if every constraint on the table is a result of the definitions of domains and keys.

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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 memecah tabel baru kolaborasi antara atribut Departement dengan Subject, Departement dengan Student atau Subject dengan Student

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Other Normal Forms

Diperoleh 3 tabel• Dept – Stud• Dept – Sub• Sub - Stud