Distributed Database Management Systems: Lecture 12

Distributed Database Management Systems: Lecture 12. The main topics covered in this chapter include: global schema architecture; GCSs in MDBS and logically integrated DDBS is different; design process moves in inverse directions, MDBS design process is bottom up, where as in logically integrated DDBS it is top-down;...

Distributed Database Management Systems

 L External

Schema

 G External Schema

Global Schema

Component Schema • • • ComponentSchema

• • •

Schema Translation Schema Integration

 G External Schema

 L External Schema

• GCSs in MDBS and logically

integrated DDBS is different

• Design process moves in inverse

directions, MDBS design process

is bottom up, where as in logically integrated DDBS it is top-down

 External

Schema  ExternalSchema

Global Schema

Component

Schema • • • ComponentSchema

Local Schema • • • SchemaLocal

Global Schema Architecture

Schema Translation

Schema Integration

Federated Schema FederatedSchema

Export Schema

Component Schema • • • ComponentSchema

Local Schema • • • SchemaLocal

Export Schema SchemaExport

 External Schema  ExternalSchema

Federated Database Architecture

Export Schema

Global Data Dictionary

• A directory is a database that

contains data about data

(meta-data)

• Called global directory in case of a

DDBS

• Contains mappings

• A single large or multiple for

different sites

• Hierarchies of DD can be built

• Location: whether to keep at a

single site or distributed

• Single site increases load on that

site

• Single copy or replication

• Replication increases availability

and reliability

• All three issues are orthogonal to

each other

• That concludes our Architecture

discussion

• Lets summarize

• Schema Design

The DDB Design concerns two major steps, Schema Design and Schema Distribution

• Schema Distribution

Distribution of Schema decides

DDB Design

• Top-Down Design Process

• Bottom-Up Design Process

System Requirements (Objectives)

Conceptual Design

Distributed Design

View Design

Local Conceptual Schemas

User Input

View Integration

User Input

• Conceptual Design is Global

Conceptual Schema

• View Design results in individual

External Schema Definition

(Global users)

• Activities so far are similar to

Centralized DB Design

• Then start the distribution activity

 External Schema  ExternalSchema

Global Schema

Component Schema • • • ComponentSchema

Bottom-Up Design Process

Distribution Design Issues

1 Why fragments

2 How should we

3 How much should be

fragmented

4 Any way to test correctness

5 Allocation Strategy

6 Required Information

• Disadvantages:

– Difficult to manage in case of

non-exclusive Fragmentation (replication)

– Maintenance of Integrity constraints

Thanks