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Welcome to chapter 2
Chapter 2 DatabaseArchetecture
Chapter 2
Archetecture
The content 1).Database Users
2).Benifits of Database
3).History of database
4).Data Model, Schema
5). Three-Schema Architecture
6). Database Architecture
Difficulty: Three-Schema Architecture
Focus on: Three-Schema Architecture
Hours:2 hours
Teaching way: ppt
Database Users
Database Designers: They are responsible to define the content, the
structure, the constraints, and functions or transactions in the database. They must communicate with the end-users and understand their needs.
End-users: They use the data for queries, reports and some of them
actually update the database content.
Database Administrator Coordinates all the activities of the database
system has a good understanding of the enterprise’s information
resources and needs. Database administrator's duties include:
Storage structure and access method definition Define the structure of the database Granting users authority to access the database Backing up data Monitoring performance and responding to changes
Design a Database
DATABASEADMINISTRATOR
Startup and Shut Down the database
Create Primary Storage Structures
Backup and Recovery
Understand the Oracle Architecture
Enroll and Monitor Users
Grant and Revoke Privileges
Manage Database Storage
Database Administrator Duties
DBA Responsibilities• Install and upgrade ORACLE
server and applications• Create primary database storage
and primary objects• Allocate system storage and plan
future storage needs• Modify the database structures• Enroll and monitor user access to
the database• Back up and recover the database• Maintain system Security• Monitor and optimize
performance
Benefits of Database Technology
- Controlling redundancy in data storage and in development and maintenance efforts.
- Sharing of data among multiple users.- Restricting unauthorized access to data.- Providing multiple interfaces to
different classes of users.- Representing complex relationships
among data.- Enforcing integrity constraints on the
database.- Providing backup and recovery services.- Potential for enforcing standards.- Flexibility to change data structures.- Reduced application development time.- Availability of up-to-date information.
Economies of scale.
Timetable
StudentAdmin
Scheduler
Payroll
Year List
Cheques
Students Course Data Lecturer Data
Timetable
StudentAdmin
Scheduler
Payroll
Year List
Cheques
Students Course Data Lecturer Data
DataBase Management System
Database
History of Database Systems
1950s and early 1960s: Data processing using magnetic tapes for storage
Tapes provide only sequential access Punched cards for input
Late 1960s and 1970s: Hard disks allow direct access to data Network and hierarchical data models in widespread use
After 1970 : Ted Codd defines the relational data model High-performance (for the era) transaction processing
Hierarchical Database Model
Logically represented by an upside down tree Each parent can have many children Each child has only one parent
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Network Database Model Each record can have multiple parents
Composed of sets Each set has owner record and member record Member may have several owners
Storage structure: linked list, dual linked list
Student dorm
students Teaching group
department
teachers
Relational Database Model
Storage structure: tables stored as files
History 1980s:
Research relational prototypes evolve into commercial systems SQL becomes industry standard
Parallel and distributed database systems Object-oriented database systems
1990s: Large decision support and data-mining applications Large multi-terabyte data warehouses Emergence of Web commerce
2000s: XML and XQuery standards Automated database administration Increasing use of highly parallel database systems Web-scale distributed data storage systems
Extending Database Capabilities
New functionality is being added to DBMSs in the following areas: Scientific Applications Image Storage and Management Audio and Video data management Data Mining Spatial data management Time Series and Historical Data Management
The above gives rise to new research and development in incorporating new data types, complex data structures, new operations and storage and indexing schemes in database systems.
Data Models A collection of tools for describing
Data structure Data operation Data constraints
Categories of data models:1.Conceptual (high-level, semantic) data models: Provide
concepts that are close to the way many users perceive data. Conceptual data models use concepts such as entities, attributes, and relationships. Entity-Relationship data model (mainly for database design)
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Slide 2-15
Categories of data models2. Physical (low-level, internal) data models: Provide concepts that de
scribe details of how data is stored in the computer by representing information such as record formats, record orderings, and access paths. An access path is a structure that makes the search for particular database records efficient.
3. Implementation (representational) data models: Provide concepts that fall between the above two, balancing user views with some computer storage details. The models used here are most frequently in traditional commercial DBMSs, and they include the widely-used relational data model, network and hierarchical ,Object-based data models (Object-oriented and Object-relational)
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Instances and Schemas
Similar to types and variables in programming languages Schema – the logical structure of the database
Example: The database consists of information about a set of customers and accounts and the relationship between them)
Analogous to type information of a variable in a program Instance – the actual content of the database at a particular
point in time Analogous to the value of a variable Student(studno,name,address) Course(courseno,lecturer)
Student(123,Bloggs,Woolton) (321,Jones,Owens)
Levels of Abstraction
Physical level: describes how a record (e.g., customer) is stored.
Logical level: describes data stored in database, and the relationships among the data.
type customer = record
customer_id : string; customer_name : string;customer_street : string;customer_city : string;
end;
View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.
View of DataAn architecture for a database system
Slide 2-19
Three-Schema Architecture
Mappings among schema levels are needed to transform requests and data. Programs refer to an external schema, and are mapped by the DBMS to the internal schema for execution.
• Logical Data Independence: The capacity to change the conceptual schema without having to change the external schemas and their application programs.
• Physical Data Independence: The capacity to change the internal schema without having to change the conceptual schema.
• When a schema at a lower level is changed, only the mappings between this schema and higher-level schemas need to be changed in a DBMS that fully supports data independence. The higher-level schemas themselves are unchanged. Hence, the application programs need not be changed since they refer to the external schemas.
Database Management System Internals
Storage management Query processing Transaction processing
Storage Management
Storage manager is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system.
The storage manager is responsible to the following tasks: Interaction with the file manager Efficient storing, retrieving and updating of data
Issues: Storage access File organization Indexing and hashing
Query Processing1. Parsing and translation
2. Optimization
3. Evaluation
Transaction Management
A transaction is a collection of operations that performs a single logical function in a database application
Transaction-management component ensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures.
Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the
consistency of the database.
Overall System Structure
Slide 2-25
DBMS Languages
• High Level or Non-procedural Languages: e.g., SQL, are set-oriented and specify what data to retrieve than how to retrieve. Also called declarative languages.
• Data Definition Language (DDL): Used by the DBA and database designers to specify the conceptual schema of a database.
• Data Manipulation Language (DML): Used to specify database retrievals and updates.
• Example: select age from student where name=‘Tom’
Database System Utilities
To perform certain functions such as:- Loading data stored in files into a database.- Backing up the database periodically on tape.- Reorganizing database file structures.- Report generation utilities.- Performance monitoring utilities.- Other functions, such as sorting , user monitoring , data compression , etc.Data dictionary / repository:- Used to store schema descriptions and other information such as design
decisions, application program descriptions, user information, usage standards, etc.
- Active data dictionary is accessed by DBMS software and users/DBA.- Passive data dictionary is accessed by users/DBA only.
Slide 2-30
DBMS Interfaces
• Stand-alone query language interfaces.• Programmer interfaces for embedding DML in
programming languages:• Pre-compiler Approach• Procedure (Subroutine) Call Approach
• User-friendly interfaces:• Menu-based, popular for browsing on the web• Forms-based, designed for naïve users• Graphics-based (Point and Click, Drag and Drop etc.)• Natural language: requests in written English• Combinations of the above
Slide 2-31
Other DBMS Interfaces
• Speech as Input (?) and Output• Web Browser as an interface• Parametric interfaces (e.g., bank tellers) using function
keys.• Interfaces for the DBA:
• Creating accounts, granting authorizations• Setting system parameters• Changing schemas or access path
Database ArchitectureThe architecture of a database systems is greatly influenced by
the underlying computer system on which the database is running: Centralized Client-server Parallel (multiple processors and disks)
Distributed
A physical centralized architecture.
Logical two-tier client/server architecture.
Physical two-tier client-server architecture.
Logical three-tier client/server architecture.
Classification of DBMSs
Based on the data model used:- Traditional: Relational, Network, Hierarchical.- Emerging: Object-oriented, Object-relational, Semi-structured
Other classifications:- Single-user (typically used with micro- computers) vs. multi-user
(most DBMSs).- Centralized (uses a single computer with one database) vs. - distributed (uses multiple computers, multiple databases)
Distributed Database Systems have now come to be known as client server based database systems because they do not support a totally distributed environment, but rather a set of database servers supporting a set of clients.
Summary
From this lecture you can learn : 1).Database Users
2).Benifits of Database
3).History of database
4).Data Model, Schema
5). Three-Schema Architecture
Any Questions?If there are any outstanding questions you can ask me one-to-one after the lecture OR privately in my office.
Exercises
1.what is three-schema architecture?