Database Management System Database System Concepts 6 th

Database Management System Database System Concepts, 6 th Ed. ©Silberschatz, Korth and Sudarshan See www. db-book. com for conditions on re-use

Database Management System (DBMS) n DBMS contains information about a particular enterprise l Collection of interrelated data l Set of programs to access the data l An environment that is both convenient and efficient to use n Database Applications: l Banking: transactions l Airlines: reservations, schedules l Universities: registration, grades l Sales: customers, products, purchases l Online retailers: order tracking, customized recommendations l Manufacturing: production, inventory, orders, supply chain l Human resources: employee records, salaries, tax deductions n Databases can be very large. n Databases touch all aspects of our lives Database System Concepts - 6 th Edition 1. 2 ©Silberschatz, Korth and Sudarshan

University Database Example n Application program examples l Add new students, instructors, and courses l Register students for courses, and generate class rosters l Assign grades to students, compute grade point averages (GPA) and generate transcripts n In the early days, database applications were built directly on top of file systems Database System Concepts - 6 th Edition 1. 3 ©Silberschatz, Korth and Sudarshan

Drawbacks of using file systems to store data l Data redundancy and inconsistency 4 Multiple l file formats, duplication of information in different files Difficulty in accessing data 4 Need to write a new program to carry out each new task l Data isolation — multiple files and formats l Integrity problems 4 Integrity constraints (e. g. , account balance > 0) become “buried” in program code rather than being stated explicitly 4 Hard Database System Concepts - 6 th Edition to add new constraints or change existing ones 1. 4 ©Silberschatz, Korth and Sudarshan

Drawbacks of using file systems to store data (Cont. ) l l Atomicity of updates 4 Failures may leave database in an inconsistent state with partial updates carried out 4 Example: Transfer of funds from one account to another should either complete or not happen at all Concurrent access by multiple users 4 Concurrent access needed for performance 4 Uncontrolled concurrent accesses can lead to inconsistencies – Example: Two people reading a balance (say 100) and updating it by withdrawing money (say 50 each) at the same time l Security problems 4 Hard to provide user access to some, but not all, data Database systems offer solutions to all the above problems Database System Concepts - 6 th Edition 1. 5 ©Silberschatz, Korth and Sudarshan

Data Models n A collection of tools for describing Data l Data relationships l Data semantics l Data constraints l n Relational model n Entity-Relationship data model (mainly for database design) n Object-based data models (Object-oriented and Object-relational) n Semistructured data model (XML) n Other older models: l l Network model Hierarchical model Database System Concepts - 6 th Edition 1. 9 ©Silberschatz, Korth and Sudarshan

Relational Model n Relational model (Chapter 2) n Example of tabular data in the relational model Columns Rows Database System Concepts - 6 th Edition 1. 10 ©Silberschatz, Korth and Sudarshan

A Sample Relational Database System Concepts - 6 th Edition 1. 11 ©Silberschatz, Korth and Sudarshan

Data Definition Language (DDL) n Specification notation for defining the database schema Example: create table instructor ( ID char(5), name varchar(20), dept_name varchar(20), salary numeric(8, 2)) n DDL compiler generates a set of table templates stored in a data dictionary n Data dictionary contains metadata (i. e. , data about data) l Database schema l Integrity constraints 4 Primary key (ID uniquely identifies instructors) 4 Referential integrity (references constraint in SQL) – e. g. dept_name value in any instructor tuple must appear in department relation l Authorization Database System Concepts - 6 th Edition 1. 13 ©Silberschatz, Korth and Sudarshan

SQL n SQL: widely used non-procedural language Example: Find the name of the instructor with ID 22222 select name from instructor where instructor. ID = ‘ 22222’ l Example: Find the ID and building of instructors in the Physics dept. select instructor. ID, department. building from instructor, department where instructor. dept_name = department. dept_name and department. dept_name = ‘Physics’ l n Application programs generally access databases through one of Language extensions to allow embedded SQL l Application program interface (e. g. , ODBC/JDBC) which allow SQL queries to be sent to a database n Chapters 3, 4 and 5 l Database System Concepts - 6 th Edition 1. 14 ©Silberschatz, Korth and Sudarshan

Database Design? n Is there any problem with this design? Database System Concepts - 6 th Edition 1. 16 ©Silberschatz, Korth and Sudarshan

Design Approaches n Normalization Theory (Chapter 8) l Formalize what designs are bad, and test for them n Entity Relationship Model (Chapter 7) l Models an enterprise as a collection of entities and relationships 4 Entity: a “thing” or “object” in the enterprise that is distinguishable from other objects – Described by a set of attributes 4 Relationship: l an association among several entities Represented diagrammatically by an entity-relationship diagram: Database System Concepts - 6 th Edition 1. 17 ©Silberschatz, Korth and Sudarshan

The Entity-Relationship Model n Models an enterprise as a collection of entities and relationships l Entity: a “thing” or “object” in the enterprise that is distinguishable from other objects 4 Described l by a set of attributes Relationship: an association among several entities n Represented diagrammatically by an entity-relationship diagram: What happened to dept_name of instructor and student? Database System Concepts - 6 th Edition 1. 18 ©Silberschatz, Korth and Sudarshan

Storage Management n 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. n The storage manager is responsible to the following tasks: l Interaction with the file manager l Efficient storing, retrieving and updating of data n Issues: l Storage access l File organization l Indexing and hashing Database System Concepts - 6 th Edition 1. 21 ©Silberschatz, Korth and Sudarshan

Query Processing 1. Parsing and translation 2. Optimization 3. Evaluation Database System Concepts - 6 th Edition 1. 22 ©Silberschatz, Korth and Sudarshan

Transaction Management n What if the system fails? n What if more than one user is concurrently updating the same data? n A transaction is a collection of operations that performs a single logical function in a database application n 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. n Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database. Database System Concepts - 6 th Edition 1. 24 ©Silberschatz, Korth and Sudarshan

Database System Internals Database System Concepts - 6 th Edition 1. 26 ©Silberschatz, Korth and Sudarshan

Database Architecture The architecture of a database systems is greatly influenced by the underlying computer system on which the database is running: n Centralized n Client-server n Parallel (multi-processor) n Distributed Database System Concepts - 6 th Edition 1. 27 ©Silberschatz, Korth and Sudarshan

History of Database Systems n 1950 s and early 1960 s: l Data processing using magnetic tapes for storage 4 Tapes l provided only sequential access Punched cards for input n Late 1960 s and 1970 s: l Hard disks allowed direct access to data l Network and hierarchical data models in widespread use l Ted Codd defines the relational data model 4 Would 4 IBM 4 UC l win the ACM Turing Award for this work Research begins System R prototype Berkeley begins Ingres prototype High-performance (for the era) transaction processing Database System Concepts - 6 th Edition 1. 28 ©Silberschatz, Korth and Sudarshan

History (cont. ) n 1980 s: Research relational prototypes evolve into commercial systems 4 SQL becomes industrial standard l Parallel and distributed database systems l Object-oriented database systems n 1990 s: l Large decision support and data-mining applications l Large multi-terabyte data warehouses l Emergence of Web commerce l n Early 2000 s: XML and XQuery standards l Automated database administration n Later 2000 s: l Giant data storage systems 4 Google Big. Table, Yahoo PNuts, Amazon, . . l Database System Concepts - 6 th Edition 1. 29 ©Silberschatz, Korth and Sudarshan

Figure 1. 02 Database System Concepts - 6 th Edition 1. 30 ©Silberschatz, Korth and Sudarshan

Figure 1. 04 Database System Concepts - 6 th Edition 1. 31 ©Silberschatz, Korth and Sudarshan

Figure 1. 06 Database System Concepts - 6 th Edition 1. 32 ©Silberschatz, Korth and Sudarshan

Data Redundancy Data redundancy is a condition created within a database or data storage technology in which the same piece of data is held in two separate places. This can mean two different fields within a single database, or two different spots in multiple software environments or platforms. ACID Properties of DBMS 1. Atomicity 2. Consistency 3. Isolation 4. Durability Database System Concepts - 6 th Edition 1. 33 ©Silberschatz, Korth and Sudarshan

Data Inconsistency and Durability Data inconsistency is a condition that occurs between files when similar data is kept in different formats in two different files, or when matching of data must be done between files. Durability. Committed data is saved by the system such that, even in the event of a failure and system restart, the data is available in its correct state. Database System Concepts - 6 th Edition 1. 34 ©Silberschatz, Korth and Sudarshan

Data Isolation and Integrity Data Isolation, in the context of databases, specifies when and how the changes implemented in an operation become visible to other parallel operations. Transaction isolation is an important part of any transactional system. It deals with consistency and completeness of data retrieved by queries unaffecting a user data by other user actions. A database acquires locks on data to maintain a high level of isolation. Data integrity refers to the overall completeness, accuracy and consistency of data. This can be indicated by the absence of alteration between two instances or between two updates of a data record, meaning data is intact and unchanged. Database System Concepts - 6 th Edition 1. 35 ©Silberschatz, Korth and Sudarshan