a. Data Models

Object-Oriented Data Models

b. Database Hardware

Database Machines

c. User Interfaces

Query by Form

Natural Language

d. Program Interfaces

Fourth-Generation Languages

e. Presentation and Display

Business Graphics, Integrating Image Technology

f. Nature of Processing

Data Communication Technology

Transaction Processing

Knowledge Processing

Object Structure

An object has associated with :

• A set of variables that contain the data for the object. The value of each variable is itself an object.
• A set of messages to which the object responds.
• A method, which is a body of code to implement each message. A method returns a value as the response to the message.

Class Hierarchy

A class object includes:

• A set-valued variable whose value is the set of all objects that are instances of the class.
• Implementation of a method for the message new, which creates a new instances of the class.

Multiple Inheritance

Object Identity 

Forms of identity:

• Value. A data value is used for identity. This is the form of identity used in relational systems.
• Name. A user-supplied name is used for identity. This is the form of identity typically used for variables in procedures. Each variable is given a name that uniquely identifies the variable regardless of the value it contains.
• Built-in. A notion of identity is built into the data model or programming language, and no user-supplied identifier is required. This is the form of identify used in object-oriented systems.

 Degree of permanence of identity:

• Intraprogram. Identity persists only during the execution of a single program or query. Examples of intraprogram identity are variable names in programming languages and tuple identifiers in SQL.
• Interprogram. Identity persists from one program execution to another. Examples of interprogram identity are relation names in a relational query language such as SQL.
• Persistent. Identity persist not only among program executions but also among structural reorganizations of the data. Relations in SQL do not have persistent identity, since a database reorganization may result in a new database scheme with relations with new names. It is the persistent form of identity that is required for object-oriented systems.

Object Containment

Physical Organization

Objects are typically represented as follows:

• Certain classes are treated as basic building-block classes that are implement directly by the computer system. Typically, the basic classes correspond to the standard programming language data types such as integer, float, character, and string.
• Instances of classes that are not basic are represented as follows:
• Variables are represented by fields of a record type. Each field contains either the object value itself, for instances of the basic classes, or the object identifier for instances of nonbasic classes.
• Set-valued variables are represented by a linked list of the objects that are members of the set.

Highly specialized data types:

• Text data. Text is usually treated as a byte string manipulated by editors and formatters.
• Audio data. Audio data is typically a digitized, compressed representation of speech that is handled by separated application software.
• Video and graphical data. Video data may be represented as a bit map or as a set of lines, boxes, and other geometric objects. Although some graphical data is often managed within the database system itself, special application software is used for many cases.

Scheme Modification

Modifications:

• Create or drop a relation.
• Add or delete attributes from a relation scheme.

The complication arises from two sources:

• Complex changes. The types of modification that can be made to an object-oriented scheme are more complex than those can be made to a relational database scheme.
• Frequent changes. The applications that motivate the user of the object-oriented model require frequent scheme changes. Design applications often involve the alteration of the structure of the item being designed.

To illustrate the complexity of object-oriented schema modification, we list several types of modification below:

• Addition of a new class. The addition of a new class in an object-oriented database involves more than the addition of a relation scheme involved in a relational database. The new class must be placed in the class/subclass hierarchy or DAG, and inheritance issues must be resolved. If the new class is not a leaf node in the hierarchy or DAG, subclasses of the new class may need to inherit variables or methods from the new class. The same applies to sub-subclasses, and so on.
• Deletion of a class. The deletion of a class in an object-oriented database requires several operations. Inheritance of variables and methods by subclasses of the deleted class must be reexamined. Any changes to a subclass may need to be propagated to sub-subclasses, and so on. Instances of the deleted class must be made instances of another class, typically a parent of deleted class.
• Modification of a class definition. A new variable or method may be defined or a variable or method definition may be deleted. As for the above cases, the definition of subclasses may be affected.
• Repositioning of classes in the hierarchy or DAG. Any restructuring of the class hierarchy of DAG has consequences on inheritance by old and new subclasses of the repositioned class.

 Among the techniques used to reduce the overhead of scheme modification are:

• Modification on access. When an object is accessed, its structure is compared with the current definition of its class. Any necessary changes are made before the object is made available. As a result, the overhead of scheme modification is spread over the accesses to objects.
• Versions of schemes. Rather than requiring that an object be modified to conform to the current definition of its class, old versions of the class definition are retained for access to old objects. The maintenance of multiple versions imposes space overhead. It also complicates the coding of methods because of the need to handle multiple versions of the class definition.

a. Engineering Design and Manufacturing

CAD systems

b. Office Information Systems

Office-by-Example  

c. Decision Support Systems (DSSs)

in Office Systems  

d. Statistical and Scientific Database Management

Micro and Macro SSDBs

 Knowledge:

• Structural knowledge
• General procedural knowledge
• Application-specific knowledge
• Enterprise-directing knowledge

Specific objectives of a knowledge-based management systems are:

1. To provide the usual database management system services to both the database and the knowledge base, including the efficient organization of large amounts of data, fast data access, concurrency control, integrity rule checking, transaction management, security enforcement, physical and logical independence, and so on.

2. To provide better user interfaces, including using natural language for queries.

3. To use knowledge-based query optimization, including use of integrity rules, database statistics, and meta-knowledge for single queries.

4. To extend optimization to multiple queries by recognizing common subexpressions and remembering query results.

5. To maintain consistency by semantic integrity checking using rule-based or logic-based techniques from artificial intelligence.

Architecture of Knowledge-Based Management systems