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Ch1
- 2. Chapter 1: Introduction
s Purpose of Database Systems
s View of Data
s Database Languages
s Relational Databases
s Database Design
s Objectbased and semistructured databases
s Data Storage and Querying
s Transaction Management
s Database Architecture
s Database Users and Administrators
s Overall Structure
s History of Database Systems
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 3. Database Management System (DBMS)
s DBMS contains information about a particular enterprise
q Collection of interrelated data
q Set of programs to access the data
q An environment that is both convenient and efficient to use
s Database Applications:
q Banking: all transactions
q Airlines: reservations, schedules
q Universities: registration, grades
q Sales: customers, products, purchases
q Online retailers: order tracking, customized recommendations
q Manufacturing: production, inventory, orders, supply chain
q Human resources: employee records, salaries, tax deductions
s Databases touch all aspects of our lives
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 4. Purpose of Database Systems
s In the early days, database applications were built directly on top of
file systems
s Drawbacks of using file systems to store data:
q Data redundancy and inconsistency
Multiple file formats, duplication of information in different files
q Difficulty in accessing data
Need to write a new program to carry out each new task
q Data isolation — multiple files and formats
q Integrity problems
Integrity constraints (e.g. account balance > 0) become
“buried” in program code rather than being stated explicitly
Hard to add new constraints or change existing ones
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 5. Purpose of Database Systems (Cont.)
s Drawbacks of using file systems (cont.)
q Atomicity of updates
Failures may leave database in an inconsistent state with partial
updates carried out
Example: Transfer of funds from one account to another should
either complete or not happen at all
q Concurrent access by multiple users
Concurrent accessed needed for performance
Uncontrolled concurrent accesses can lead to inconsistencies
– Example: Two people reading a balance and updating it at the
same time
q Security problems
Hard to provide user access to some, but not all, data
s Database systems offer solutions to all the above problems
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 6. Levels of Abstraction
s Physical level: describes how a record (e.g., customer) is stored.
s 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 : integer;
end;
s View level: application programs hide details of data types. Views can
also hide information (such as an employee’s salary) for security
purposes.
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 7. View of Data
An architecture for a database system
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 8. Instances and Schemas
s Similar to types and variables in programming languages
s Schema – the logical structure of the database
q Example: The database consists of information about a set of customers and
accounts and the relationship between them)
q Analogous to type information of a variable in a program
q Physical schema: database design at the physical level
q Logical schema: database design at the logical level
s Instance – the actual content of the database at a particular point in time
q Analogous to the value of a variable
s Physical Data Independence – the ability to modify the physical schema without
changing the logical schema
q Applications depend on the logical schema
q In general, the interfaces between the various levels and components should be
well defined so that changes in some parts do not seriously influence others.
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 9. Data Models
s A collection of tools for describing
q Data
q Data relationships
q Data semantics
q Data constraints
s Relational model
s EntityRelationship data model (mainly for database design)
s Objectbased data models (Objectoriented and Objectrelational)
s Semistructured data model (XML)
s Other older models:
q Network model
q Hierarchical model
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 10. Data Manipulation Language (DML)
s Language for accessing and manipulating the data organized by the
appropriate data model
q DML also known as query language
s Two classes of languages
q Procedural – user specifies what data is required and how to get
those data
q Declarative (nonprocedural) – user specifies what data is
required without specifying how to get those data
s SQL is the most widely used query language
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 11. Data Definition Language (DDL)
s Specification notation for defining the database schema
Example: create table account (
accountnumber char(10),
balance integer)
s DDL compiler generates a set of tables stored in a data dictionary
s Data dictionary contains metadata (i.e., data about data)
q Database schema
q Data storage and definition language
Specifies the storage structure and access methods used
q Integrity constraints
Domain constraints
Referential integrity (references constraint in SQL)
Assertions
q Authorization
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 12. Relational Model
Attributes
s Example of tabular data in the relational model
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 14. SQL
s SQL: widely used nonprocedural language
q Example: Find the name of the customer with customerid 192837465
select customer.customer_name
from customer
where customer.customer_id = ‘192837465’
q Example: Find the balances of all accounts held by the customer with
customerid 192837465
select account.balance
from depositor, account
where depositor.customer_id = ‘192837465’ and
depositor.account_number = account.account_number
s Application programs generally access databases through one of
q Language extensions to allow embedded SQL
q Application program interface (e.g., ODBC/JDBC) which allow SQL
queries to be sent to a database
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 15. Database Design
The process of designing the general structure of the database:
s Logical Design – Deciding on the database schema. Database design
requires that we find a “good” collection of relation schemas.
q Business decision – What attributes should we record in the
database?
q Computer Science decision – What relation schemas should we
have and how should the attributes be distributed among the various
relation schemas?
s Physical Design – Deciding on the physical layout of the database
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 16. The EntityRelationship Model
s Models an enterprise as a collection of entities and relationships
q Entity: a “thing” or “object” in the enterprise that is distinguishable
from other objects
Described by a set of attributes
q Relationship: an association among several entities
s Represented diagrammatically by an entityrelationship diagram:
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 17. ObjectRelational Data Models
s Extend the relational data model by including object orientation and
constructs to deal with added data types.
s Allow attributes of tuples to have complex types, including nonatomic
values such as nested relations.
s Preserve relational foundations, in particular the declarative access to
data, while extending modeling power.
s Provide upward compatibility with existing relational languages.
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 18. XML: Extensible Markup Language
s Defined by the WWW Consortium (W3C)
s Originally intended as a document markup language not a
database language
s The ability to specify new tags, and to create nested tag structures
made XML a great way to exchange data, not just documents
s XML has become the basis for all new generation data interchange
formats.
s A wide variety of tools is available for parsing, browsing and
querying XML documents/data
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 19. Storage Management
s Storage manager is a program module that provides the interface
between the lowlevel data stored in the database and the application
programs and queries submitted to the system.
s The storage manager is responsible to the following tasks:
q Interaction with the file manager
q Efficient storing, retrieving and updating of data
s Issues:
q Storage access
q File organization
q Indexing and hashing
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 20. Query Processing
1. Parsing and translation
2. Optimization
3. Evaluation
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 21. Query Processing (Cont.)
s Alternative ways of evaluating a given query
q Equivalent expressions
q Different algorithms for each operation
s Cost difference between a good and a bad way of evaluating a query can
be enormous
s Need to estimate the cost of operations
q Depends critically on statistical information about relations which the
database must maintain
q Need to estimate statistics for intermediate results to compute cost of
complex expressions
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 22. Transaction Management
s A transaction is a collection of operations that performs a single
logical function in a database application
s Transactionmanagement 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.
s Concurrencycontrol manager controls the interaction among the
concurrent transactions, to ensure the consistency of the database.
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 23. Database Architecture
The architecture of a database systems is greatly influenced by
the underlying computer system on which the database is running:
s Centralized
s Clientserver
s Parallel (multiprocessor)
s Distributed
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 24. Database Users
Users are differentiated by the way they expect to interact with
the system
s Application programmers – interact with system through DML calls
s Sophisticated users – form requests in a database query language
s Specialized users – write specialized database applications that do
not fit into the traditional data processing framework
s Naïve users – invoke one of the permanent application programs that
have been written previously
q Examples, people accessing database over the web, bank tellers,
clerical staff
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 25. Database Administrator
s Coordinates all the activities of the database system; the
database administrator has a good understanding of the
enterprise’s information resources and needs.
s Database administrator's duties include:
q Schema definition
q Storage structure and access method definition
q Schema and physical organization modification
q Granting user authority to access the database
q Specifying integrity constraints
q Acting as liaison with users
q Monitoring performance and responding to changes in
requirements
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 27. History of Database Systems
s 1950s and early 1960s:
q Data processing using magnetic tapes for storage
Tapes provide only sequential access
q Punched cards for input
s Late 1960s and 1970s:
q Hard disks allow direct access to data
q Network and hierarchical data models in widespread use
q Ted Codd defines the relational data model
Would win the ACM Turing Award for this work
IBM Research begins System R prototype
UC Berkeley begins Ingres prototype
q Highperformance (for the era) transaction processing
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan
- 28. History (cont.)
s 1980s:
q Research relational prototypes evolve into commercial systems
SQL becomes industrial standard
q Parallel and distributed database systems
q Objectoriented database systems
s 1990s:
q Large decision support and datamining applications
q Large multiterabyte data warehouses
q Emergence of Web commerce
s 2000s:
q XML and XQuery standards
q Automated database administration
Database System Concepts 5th Edition, May 23, 2005 1.<number> ©Silberschatz, Korth and Sudarshan