Database Systems: Design, Implementation, and Management
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6 Lecture 9 Database Design DBLC and Centralized vs Decentralize Design www.getmyuni.com
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Transcript of Database Systems: Design, Implementation, and Management
6
Lecture 9
Database Design
DBLC and Centralized vs Decentralize Design
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• Data
– Raw facts stored in databases
– Need additional processing to become useful
• Information
– Required by decision maker
– Data processed and presented in a meaningful
form
– Transformation
Changing Data into Information
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• Database
– Carefully designed and constructed repository of
facts
– Part of an information system
• Information System
– Provides data collection, storage, and retrieval
– Facilitates data transformation
– Components include:
• People
• Hardware
• Software–Database(s)
–Application programs
–Procedures
The Information System
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• System Analysis
– Establishes need and extent of an information
system
• Systems development
– Process of creating information system
• Database development
– Process of database design and implementation
– Creation of database models
– Implementation
• Creating storage structure
• Loading data into database
• Providing for data management
The Information System (Con’t.)
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Figure 6.2
Systems Development Life Cycle
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Figure 6.3
Database Lifecycle (DBLC)
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Phase 1: Database Initial Study
• Purposes
– Analyze company situation
• Operating environment
• Organizational structure
– Define problems and constraints
– Define objectives
– Define scope and boundaries
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Initial Study Activities
Figure 6.4
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Phase 2: Database Design
• Most Critical DBLC phase
• Makes sure final product meets requirements
• Focus on data requirements
• Subphases
– Create conceptual design
– DBMS software selection
– Create logical design
– Create physical design
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Two Views of Data
Figure 6.5
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I. Conceptual Design
• Data modeling creates abstract data structure to
represent real-world items
• High level of abstraction
• Four steps
– Data analysis and requirements
– Entity relationship modeling and normalization
– Data model verification
– Distributed database design
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Data analysis and Requirements
• Focus on:
– Information needs
– Information users
– Information sources
– Information constitution
• Data sources
– Developing and gathering end-user data views
– Direct observation of current system
– Interfacing with systems design group
• Business rules
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Entity Relationship
Modeling and Normalization
Table 6.2
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E-R Modeling is Iterative
Figure 6.8
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Concept Design: Tools and Sources
Figure 6.9
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Data Model Verification
• E-R model is verified against proposed system
processes
– End user views and required transactions
– Access paths, security, concurrency control
– Business-imposed data requirements and
constraints
• Reveals additional entity and attribute details
• Define major components as modules
– Cohesivity
– Coupling
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E-R Model Verification Process
Table 6.4
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Iterative Process of Verification
Figure 6.10
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Distributed Database Design
• Design portions in different physical locations
• Development of data distribution and allocation
strategies
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II. DBMS Software Selection
• DBMS software selection is critical
• Advantages and disadvantages need study
• Factors affecting purchasing decision
– Cost
– DBMS features and tools
– Underlying model
– Portability
– DBMS hardware requirements
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III. Logical Design
• Translates conceptual design into internal model
• Maps objects in model to specific DBMS
constructs
• Design components
– Tables
– Indexes
– Views
– Transactions
– Access authorities
– Others
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IV. Physical Design
• Selection of data storage and access
characteristics
– Very technical
– More important in older hierarchical and network
models
• Becomes more complex for distributed systems
• Designers favor software that hides physical
details
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Physical Organization
Figure 6.12
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Phase 3: Implementation and Loading
• Creation of special storage-related constructs
to house end-user tables
• Data loaded into tables
• Other issues
– Performance
– Security
– Backup and recovery
– Integrity
– Company standards
– Concurrency controls
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Phase 4: Testing and Evaluation
• Database is tested and fine-tuned for
performance, integrity, concurrent access, and
security constraints
• Done in parallel with application programming
• Actions taken if tests fail
– Fine-tuning based on reference manuals
– Modification of physical design
– Modification of logical design
– Upgrade or change DBMS software or hardware
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Phase 5: Operation
• Database considered operational
• Starts process of system evaluation
• Unforeseen problems may surface
• Demand for change is constant
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Phase 6: Maintenance and Evaluation
• Preventative maintenance
• Corrective maintenance
• Adaptive maintenance
• Assignment of access permissions
• Generation of database access statistics to
monitor performance
• Periodic security audits based on system-
generated statistics
• Periodic system usage-summaries
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DB Design Strategy Notes
• Top-down
– 1) Identify data sets
– 2) Define data elements
• Bottom-up
– 1) Identify data elements
– 2) Group them into data sets
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Top-Down vs. Bottom-Up
Figure 6.14
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Centralized vs. Decentralized Design
• Centralized design
– Typical of simple databases
– Conducted by single person or small team
• Decentralized design
– Larger numbers of entities and complex relations
– Spread across multiple sites
– Developed by teams
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Centralized Design
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Decentralized Design
Figure 6.16
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Centralized vs. Decentralized Design
(continued)
• Aggregation process
– Requires designer to create single model in which
various aggregation problems must be addressed:
• Synonyms and homonyms
• Entity and entity subtypes
• Conflicting object definitions
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Centralized vs. Decentralized Design
(continued)
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