Chapter 1: Introduction  Database System Concepts, 5th Ed.       ©Silberschatz, Korth and Sudarshan  See www.db-book.com f...
Chapter 1: Introduction             s Purpose of Database Systems             s Database Languages             s Relationa...
Database Management System                                 (DBMS)             s DBMS contains information about a particul...
Purpose of Database Systems             s In the early days, database applications were built directly on top of          ...
Purpose of Database Systems                                   (Cont.)             s Drawbacks of using file systems (cont....
Levels of Abstraction             s Physical level: describes how a record (e.g., customer) is stored.             s Logic...
View of Data            An architecture for a database systematabase System Concepts - 5 th Edition, May 23, 2005   1.7   ...
Instances and Schemas             s    Similar to types and variables in programming languages             s    Schema – t...
Data Models             s A collection of tools for describing                    q Data                    q Data relatio...
Data Manipulation Language (DML)             s Language for accessing and manipulating the data organized by the          ...
Data Definition Language (DDL)             s Specification notation for defining the database schema                   Exa...
Relational Model                                                                             Attributes             s Exam...
A Sample Relational Databaseatabase System Concepts - 5 th Edition, May 23, 2005   1.13   ©Silberschatz, Korth and Sudarshan
SQL             s SQL: widely used non-procedural language                    q   Example: Find the name of the customer w...
Database Design             The process of designing the general structure of the database:             s Logical Design –...
The Entity-Relationship Model             s Models an enterprise as a collection of entities and relationships            ...
Other Data Models             s Object-oriented data model             s Object-relational data modelatabase System Concep...
Database Application Architectures                                                              (web browser)             ...
Database Management System                                Internals             s Storage management             s Query p...
Storage Management             s Storage manager is a program module that provides the interface                  between ...
Query Processing             1. Parsing and translation             2. Optimization             3. Evaluationatabase Syste...
Query Processing (Cont.)             s Alternative ways of evaluating a given query                    q   Equivalent expr...
Transaction Management             s A transaction is a collection of operations that performs a single                  l...
Overall System Structureatabase System Concepts - 5 th Edition, May 23, 2005   1.24   ©Silberschatz, Korth and Sudarshan
History of Database Systems             s 1950s and early 1960s:                   q    Data processing using magnetic tap...
History (cont.)             s 1980s:                   q    Research relational prototypes evolve into commercial systems ...
End of Chapter 1Database System Concepts, 5th Ed.     ©Silberschatz, Korth and SudarshanSee www.db-book.com for conditions...
Database Users             Users are differentiated by the way they expect to interact with             the system        ...
Database Administrator             s Coordinates all the activities of the database system                    q   has a go...
Database Architecture             The architecture of a database systems is greatly influenced by              the underly...
Object-Relational Data Models             s Extend the relational data model by including object orientation and          ...
XML: Extensible Markup Language             s Defined by the WWW Consortium (W3C)             s Originally intended as a d...
Figure 1.4atabase System Concepts - 5 th Edition, May 23, 2005      1.33      ©Silberschatz, Korth and Sudarshan
Figure 1.7atabase System Concepts - 5 th Edition, May 23, 2005      1.34      ©Silberschatz, Korth and Sudarshan
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Introduction To DBMS

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Introduction To DBMS

  1. 1. Chapter 1: Introduction Database System Concepts, 5th Ed. ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use
  2. 2. Chapter 1: Introduction s Purpose of Database Systems s Database Languages s Relational Databases s Database Design s Data Models s Database Internals s Database Users and Administrators s Overall Structure s History of Database Systemsatabase System Concepts - 5 th Edition, May 23, 2005 1.2 ©Silberschatz, Korth and Sudarshan
  3. 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 livesatabase System Concepts - 5 th Edition, May 23, 2005 1.3 ©Silberschatz, Korth and Sudarshan
  4. 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 onesatabase System Concepts - 5 th Edition, May 23, 2005 1.4 ©Silberschatz, Korth and Sudarshan
  5. 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 problemsatabase System Concepts - 5 th Edition, May 23, 2005 1.5 ©Silberschatz, Korth and Sudarshan
  6. 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 : string; 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.atabase System Concepts - 5 th Edition, May 23, 2005 1.6 ©Silberschatz, Korth and Sudarshan
  7. 7. View of Data An architecture for a database systematabase System Concepts - 5 th Edition, May 23, 2005 1.7 ©Silberschatz, Korth and Sudarshan
  8. 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.atabase System Concepts - 5 th Edition, May 23, 2005 1.8 ©Silberschatz, Korth and Sudarshan
  9. 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 Entity-Relationship data model (mainly for database design) s Object-based data models (Object-oriented and Object-relational) s Semistructured data model (XML) s Other older models: q Network model q Hierarchical modelatabase System Concepts - 5 th Edition, May 23, 2005 1.9 ©Silberschatz, Korth and Sudarshan
  10. 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 languageatabase System Concepts - 5 th Edition, May 23, 2005 1.10 ©Silberschatz, Korth and Sudarshan
  11. 11. Data Definition Language (DDL) s Specification notation for defining the database schema Example: create table account ( account_number char(10), branch_name 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 (e.g. branch_name must correspond to a valid branch in the branch table) q Authorizationatabase System Concepts - 5 th Edition, May 23, 2005 1.11 ©Silberschatz, Korth and Sudarshan
  12. 12. Relational Model Attributes s Example of tabular data in the relational modelatabase System Concepts - 5 th Edition, May 23, 2005 1.12 ©Silberschatz, Korth and Sudarshan
  13. 13. A Sample Relational Databaseatabase System Concepts - 5 th Edition, May 23, 2005 1.13 ©Silberschatz, Korth and Sudarshan
  14. 14. SQL s SQL: widely used non-procedural language q Example: Find the name of the customer with customer-id 192-83-7465 select customer.customer_name from customer where customer.customer_id = ‘192-83-7465’ q Example: Find the balances of all accounts held by the customer with customer-id 192-83-7465 select account.balance from depositor, account where depositor.customer_id = ‘192-83-7465’ 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 databaseatabase System Concepts - 5 th Edition, May 23, 2005 1.14 ©Silberschatz, Korth and Sudarshan
  15. 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 databaseatabase System Concepts - 5 th Edition, May 23, 2005 1.15 ©Silberschatz, Korth and Sudarshan
  16. 16. The Entity-Relationship 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 entity-relationship diagram:atabase System Concepts - 5 th Edition, May 23, 2005 1.16 ©Silberschatz, Korth and Sudarshan
  17. 17. Other Data Models s Object-oriented data model s Object-relational data modelatabase System Concepts - 5 th Edition, May 23, 2005 1.17 ©Silberschatz, Korth and Sudarshan
  18. 18. Database Application Architectures (web browser) Old Modernatabase System Concepts - 5 th Edition, May 23, 2005 1.18 ©Silberschatz, Korth and Sudarshan
  19. 19. Database Management System Internals s Storage management s Query processing s Transaction processingatabase System Concepts - 5 th Edition, May 23, 2005 1.19 ©Silberschatz, Korth and Sudarshan
  20. 20. Storage Management s 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. 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 hashingatabase System Concepts - 5 th Edition, May 23, 2005 1.20 ©Silberschatz, Korth and Sudarshan
  21. 21. Query Processing 1. Parsing and translation 2. Optimization 3. Evaluationatabase System Concepts - 5 th Edition, May 23, 2005 1.21 ©Silberschatz, Korth and Sudarshan
  22. 22. 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 expressionsatabase System Concepts - 5 th Edition, May 23, 2005 1.22 ©Silberschatz, Korth and Sudarshan
  23. 23. Transaction Management s A transaction is a collection of operations that performs a single logical function in a database application s 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. s Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database.atabase System Concepts - 5 th Edition, May 23, 2005 1.23 ©Silberschatz, Korth and Sudarshan
  24. 24. Overall System Structureatabase System Concepts - 5 th Edition, May 23, 2005 1.24 ©Silberschatz, Korth and Sudarshan
  25. 25. 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 High-performance (for the era) transaction processingatabase System Concepts - 5 th Edition, May 23, 2005 1.25 ©Silberschatz, Korth and Sudarshan
  26. 26. History (cont.) s 1980s: q Research relational prototypes evolve into commercial systems  SQL becomes industry standard q Parallel and distributed database systems q Object-oriented database systems s 1990s: q Large decision support and data-mining applications q Large multi-terabyte data warehouses q Emergence of Web commerce s 2000s: q XML and XQuery standards q Automated database administration q Increasing use of highly parallel database systems q Web-scale distributed data storage systemsatabase System Concepts - 5 th Edition, May 23, 2005 1.26 ©Silberschatz, Korth and Sudarshan
  27. 27. End of Chapter 1Database System Concepts, 5th Ed. ©Silberschatz, Korth and SudarshanSee www.db-book.com for conditions on re-use
  28. 28. 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 Naï ve users – invoke one of the permanent application programs that have been written previously q Examples, people accessing database over the web, bank tellers, clerical staffatabase System Concepts - 5 th Edition, May 23, 2005 1.28 ©Silberschatz, Korth and Sudarshan
  29. 29. Database Administrator s Coordinates all the activities of the database system q has a good understanding of the enterprise’s information resources and needs. s Database administrators duties include: q Storage structure and access method definition q Schema and physical organization modification q Granting users authority to access the database q Backing up data q Monitoring performance and responding to changes  Database tuningatabase System Concepts - 5 th Edition, May 23, 2005 1.29 ©Silberschatz, Korth and Sudarshan
  30. 30. 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 Client-server s Parallel (multiple processors and disks) s Distributedatabase System Concepts - 5 th Edition, May 23, 2005 1.30 ©Silberschatz, Korth and Sudarshan
  31. 31. Object-Relational 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 non-atomic 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.atabase System Concepts - 5 th Edition, May 23, 2005 1.31 ©Silberschatz, Korth and Sudarshan
  32. 32. 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/dataatabase System Concepts - 5 th Edition, May 23, 2005 1.32 ©Silberschatz, Korth and Sudarshan
  33. 33. Figure 1.4atabase System Concepts - 5 th Edition, May 23, 2005 1.33 ©Silberschatz, Korth and Sudarshan
  34. 34. Figure 1.7atabase System Concepts - 5 th Edition, May 23, 2005 1.34 ©Silberschatz, Korth and Sudarshan

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