1 Pertemuan 6 The structure part of object data model (Lanjutan) Matakuliah: M0174/OBJECT ORIENTED DATABASE Tahun: 2005 Versi: 1/0

2 Learning Outcomes Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu : Mahasiswa dapat Menjelaskan struktur object data model Lanjutan (C2)

3 Outline Materi Object types Representation of composite entities

4 Object types Object which have the same characteristic can be categorized into object type. Each object is an instance of the object type on which it was defined. The set of all instance of an object type is called the object type’s extent. The new object are created using a operation called ‘new’ on an object which is an instance of a special type called ObjectFactory.

5 Object types When designing an object database it is necessary to define an object type for each set of similar entities that are to be represented in the database. The set of object type definition for database is called the object database schema.

6 Object types Definition of an Object Types –An object type definition is consist in three parts: Type Properties Instance Properties Instance Operation –Note that an object type definition doesn’t provide a complete definition of the object type, since it doesn’t define what the operations on instance do.

7 Object types –The object data model distinguishes between two aspects of an object type: The type’s interface: this first aspect is the object type abstract appearance. An interface of an object type defines only information relating to the behavior of the type instance. It doesn’t provide the additional information necessary to create instance of the type. Object creation: the second aspect is the ability to create object which are instance of the object type. A type which can be instantiated is defined by a class definition.

8 Object types Notation for Denoting Object Type –We shall use two notations for describing object type, one graphical and the other textual

9 Object types

10 Object types Object Type Properties –Object types are themselves entities within object database system and are represented as objects. –This type of object is called a meta object, because it describes the characteristics of other objects. –The data contained in meta objects is called metadata. –The meta objects collectively define the object database schema and are used by the ODBMS to define and access objects contained in object database.

11 Object types –The metadata is stored in schema repository for use by tools and application program. –The meta objects which represent an object type have properties of their own. The values for these are specified in the type properties part of a class definition

12 Object types –The following properties can be specified: Supertype: the supertype of an interface or class Extender: the class that is extended by the specified object type Extent: the extent of an object type is the collections of its instance. Key: the instance properties that are to act as object key

13 Object types Instance Properties –An object type instance properties are the attributes and relationships of the instance of the object type. –Each attribute has a name and a type which defines the set of values that can be assigned to the attribute.

14 Object types –An object type instance properties are the attributes and relationships of the instance of the object type. –Each attribute has a name and a type which defines the set of values that can be assigned to the attribute.

15 Object types Instance Operation –Each instance operation has a name and type. An operation type define the types of the objects accepted as parameters and the type of the object returned by operation is a operation value. –Each operation has a meaning or semantic. The semantic of an operation is a declaration of what is does when it is executed.

16 Representation of composite entities Collection Object Type –Set A set is an unordered collection of distinct objects of the same type. –Bag A bag is an unordered collection of objects of the same type, but not necessary distinct. –List A list is an ordered bag. Object is in list are in a sequence. All objects in list are the same type.

17 Representation of composite entities –Array An array is a collection of objects in which each object is stored at a particular position. However position in the array may be empty. –Dictionary A dictionary is a set of structure, each of which is an object pair. A dictionary may be thought of as a list lookup table. The first object in a pair acts as a key for accessing the second

18 SUMMARY Objects with the same characteristics can be categorized into object types An object type together with an implementation is called an implementation class An object type can be defined in one of three ways