Upon completion of this Unit, the students will be introduced to the following

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1 Instructional Objectives Upon completion of this Unit, the students will be introduced to the following The meaning of the term database. Meaning of the term Database Management System (DBMS). The typical functions of a DBMS. Major components of the DBMS environment. The personnel involved in the DBMS environment. History of the development of database systems. Advantages and disadvantages of database systems. Able to answer the problems posted below: How did database software evolve? What is a database? What are the primary features of a database? What is a DBMS? What are the advantages of using a DBMS? What are the disadvantages of using a DBMS? Describe a typical system architecture for DBMS Explain about : Database Administrator, Database User What is data independence? Why is data independence important? What facility are provided by the DBMS to achieve Physical and Logical data independence? What are the database languages commonly used? What are the different data models? Outline the ANSI-SPARC 3-level DBMS architecture. Distinguish clearly between the levels What are the advantages of DBMS over conventional file systems? Briefly explain the 3 levels of data abstraction and the inter-relationship among these levels What are the responsibilities of a database manager and a database administrator? Explain the problems that would arise if the responsibility were not met What is the difference between database schema and a database state? A major purpose of a database system is to provide users with an abstract view of the data." Do you agree? Why? What is the difference between logical and physical views of data stored in a database? What are the reasons for making such distinctions? 1

2 Fundamentals Database Management System (DBMS) DBMS contains information about a particular enterprise Collection of interrelated data Set of programs to access the data An environment that is both convenient and efficient to use Database Applications: Banking: all transactions Airlines: reservations, schedules Universities: registration, grades Sales: customers, products, purchases Online retailers: order tracking, customized recommendations Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions Databases touch all aspects of our lives Purpose of Database Systems In the early days, database applications were built directly on top of file systems Drawbacks of using file systems to store data: Data redundancy and inconsistency Multiple file formats, duplication of information in different files Difficulty in accessing data Need to write a new program to carry out each new task Data isolation multiple files and formats 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 2

3 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 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 Security problems Hard to provide user access to some, but not all, data Database systems offer solutions to all the above problems 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 : integer; end; View level: application programs hide details of data types. Views can also hide information (such as an employee s salary) for security purposes. 3

View of Data 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

4 View of Data 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 Physical schema: database design at the physical level Logical schema: database design at the logical level Instance the actual content of the database at a particular point in time Analogous to the value of a variable Physical Data Independence the ability to modify the physical schema without changing the logical schema Applications depend on the logical schema 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. 4

5 Data Models A collection of tools for describing Data Data relationships Data semantics Data constraints Relational model Entity-Relationship data model (mainly for database design) Object-based data models (Object-oriented and Object-relational) Semistructured data model (XML) Other older models: Network model Hierarchical model Data Manipulation Language (DML) Language for accessing and manipulating the data organized by the appropriate data model DML also known as query language Two classes of languages Procedural user specifies what data is required and how to get those data Declarative (nonprocedural) user specifies what data is required without specifying how to get those data SQL is the most widely used query language Data Definition Language (DDL) Specification notation for defining the database schema Example: create table account ( account-number char(10), balance integer) DDL compiler generates a set of tables stored in a data dictionary Data dictionary contains metadata (i.e., data about data) Database schema Data storage and definition language Specifies the storage structure and access methods used Integrity constraints Domain constraints Referential integrity (references constraint in SQL) Assertions Authorization 5

6 Relational Model Example of tabular data in the relational model A Sample Relational Database SQL SQL: widely used non-procedural language Example: Find the name of the customer with customer-id select customer.customer_name from customer where customer.customer_id = Example: Find the balances of all accounts held by the customer with customer-id

select account.balance from depositor, account where depositor.customer_id = 192-83-7465 and depositor.account_number = account.

7 select account.balance from depositor, account where depositor.customer_id = and depositor.account_number = account.account_number Application programs generally access databases through one of Language extensions to allow embedded SQL Application program interface (e.g., ODBC/JDBC) which allow SQL queries to be sent to a database Database Design The process of designing the general structure of the database: Logical Design Deciding on the database schema. Database design requires that we find a good collection of relation schemas. Business decision What attributes should we record in the database? Computer Science decision What relation schemas should we have and how should the attributes be distributed among the various relation schemas? Physical Design Deciding on the physical layout of the database The Entity-Relationship Model Models an enterprise as a collection of entities and relationships Entity: a thing or object in the enterprise that is distinguishable from other objects Described by a set of attributes Relationship: an association among several entities Represented diagrammatically by an entity-relationship diagram: 7

8 Object-Relational Data Models Extend the relational data model by including object orientation and constructs to deal with added data types. Allow attributes of tuples to have complex types, including non-atomic values such as nested relations. Preserve relational foundations, in particular the declarative access to data, while extending modeling power. Provide upward compatibility with existing relational languages. XML: Extensible Markup Language Defined by the WWW Consortium (W3C) Originally intended as a document markup language not a database language The ability to specify new tags, and to create nested tag structures made XML a great way to exchange data, not just documents XML has become the basis for all new generation data interchange formats. A wide variety of tools is available for parsing, browsing and querying XML documents/data 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 Processing 1. Parsing and translation 2. Optimization 3. Evaluation Alternative ways of evaluating a given query Equivalent expressions Different algorithms for each operation Cost difference between a good and a bad way of evaluating a query can be enormous Need to estimate the cost of operations 8

Depends critically on statistical information about relations which the database must maintain Need to estimate statistics for intermediate results to compute cost of complex expressions Transaction

9 Depends critically on statistical information about relations which the database must maintain Need to estimate statistics for intermediate results to compute cost of complex expressions 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. Database Architecture The architecture of a database systems is greatly influenced by The underlying computer system on which the database is running: Centralized Client-server Parallel (multi-processor) Distributed 9

10 Database Users Users are differentiated by the way they expect to interact with the system Application programmers interact with system through DML calls Sophisticated users form requests in a database query language Specialized users write specialized database applications that do not fit into the traditional data processing framework Naïve users invoke one of the permanent application programs that have been written previously Examples, people accessing database over the web, bank tellers, clerical staff Database Administrator Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise s information resources and needs. Database administrator's duties include: Schema definition Storage structure and access method definition Schema and physical organization modification Granting user authority to access the database Specifying integrity constraints Acting as liaison with users Monitoring performance and responding to changes in requirements 10

Overall System Structure 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

11 Overall System Structure 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 Ted Codd defines the relational data model Would win the ACM Turing Award for this work 11

IBM Research begins System R prototype UC Berkeley begins Ingres prototype High-performance (for the era) transaction processing 1980s: Research relational prototypes evolve into commercial systems

12 IBM Research begins System R prototype UC Berkeley begins Ingres prototype High-performance (for the era) transaction processing 1980s: Research relational prototypes evolve into commercial systems SQL becomes industrial 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 Entity-relationship model A sample ER diagram In software engineering, an Entity-Relationship Model (ERM) is an abstract and conceptual representation of data. Entity-relationship modeling is a database modeling method, used to produce a type of conceptual schema or semantic data model of a system, often a relational database, and its requirements in a top-down fashion. Diagrams created using this process are called entity-relationship diagrams, or ER diagrams or ERDs for short. 12

13 Overview The first stage of information system design uses these models during the requirements analysis to describe information needs or the type of information that is to be stored in a database. The data modeling technique can be used to describe any ontology (i.e. an overview and classifications of used terms and their relationships) for a certain universe of discourse (i.e. area of interest). In the case of the design of an information system that is based on a database, the conceptual data model is, at a later stage (usually called logical design), mapped to a logical data model, such as the relational model; this in turn is mapped to a physical model during physical design. Note that sometimes, both of these phases are referred to as "physical design". There are a number of conventions for entity-relationship diagrams (ERDs). The classical notation is described in the remainder of this article, and mainly relates to conceptual modeling. There are a range of notations more typically employed in logical and physical database design. Connection Two related entities An entity with an attribute A relationship with an attribute An entity may be defined as a thing which is recognized as being capable of an independent existence and which can be uniquely identified. An entity is an abstraction from the complexities of some domain. When we speak of an entity we normally speak of some aspect of the real world which can be distinguished from other aspects of the real world. An entity may be a physical object such as a house or a car, an event such as a house sale or a car service, or a concept such as a customer transaction or order. Although the term entity is the one most commonly used, following Chen we should really distinguish between an entity and an entity-type. An entity-type is a category. An entity, strictly speaking, is an instance of a given entity-type. There are usually many instances of an entity-type. Because the term entity-type is somewhat cumbersome, most people tend to use the term entity as a synonym for this term. Entities can be thought of as nouns. Examples: a computer, an employee, a song, a mathematical theorem. Entities are represented as rectangles. 13

14 A relationship captures how two or more entities are related to one another. Relationships can be thought of as verbs, linking two or more nouns. Examples: an owns relationship between a company and a computer, a supervises relationship between an employee and a department, a performs relationship between an artist and a song, a proved relationship between a mathematician and a theorem. Relationships are represented as diamonds, connected by lines to each of the entities in the relationship. The model's linguistic aspect described above is utilized in the database query language ERROL. Entities and relationships can both have attributes. Examples: an employee entity might have a Social Security Number (SSN) attribute; the proved relationship may have a date attribute. Attributes are represented as ellipses connected to their owning entity sets by a line. Every entity (unless it is a weak entity) must have a minimal set of uniquely identifying attributes, which is called the entity's primary key. Entity-relationship diagrams don't show single entities or single instances of relations. Rather, they show entity sets and relationship sets. Example: a particular song is an entity. The collection of all songs in a database is an entity set. The eaten relationship between a child and her lunch is a single relationship. The set of all such child-lunch relationships in a database is a relationship set. Lines are drawn between entity sets and the relationship sets they are involved in. If all entities in an entity set must participate in the relationship set, a thick or double line is drawn. This is called a participation constraint. If each entity of the entity set can participate in at most one relationship in the relationship set, an arrow is drawn from the entity set to the relationship set. This is called a key constraint. To indicate that each entity in the entity set is involved in exactly one relationship, a thick arrow is drawn. ER diagramming tools There are many ER diagramming tools. Some of the proprietary ER diagramming tools are ARIS, Avolution, dbforge Studio for MySQL, DeZign for Databases, ConceptDraw, ER/Studio, Devgems Data Modeler, ERwin, MEGA International, Metastorm ProVision[1], OmniGraffle, Oracle Designer, PowerDesigner, Rational Rose, SmartDraw, Sparx Enterprise Architect, SQLyog, Toad Data Modeler, Microsoft Visio, and Visual Paradigm. A freeware ER tool that can generate database and application layer code (webservices) is the RISE Editor. 14

is called. a. Data dependence b. Data independence c. Database schema d. Data directory 2.

15 Objective Questions 1. The ability to modify a scheme definition in one level without affecting a scheme definition in a higher level is called. a. Data dependence b. Data independence c. Database schema d. Data directory 2. Which users interact with the system without writing programs? a. Sophisticated b. Naive c. Application d. Specialized 3. The Entity-Relationship data model is an example of implementation data models a. True b. False 15

16 4. A language you can use to define tables, schemas, attribute domains and constraints is called. a. DDL b. DML c. SDL d. VDL 5. Which is used to specify database retrievals and updates? a. DDL b. DML c. SDL d. VDL 6. A collection of concepts for describing data is a. Data model b. Relation c. Instance d. Meta-data 7. What is a database? a. An integrated collection of data organized to meet the needs of one or more users b. A place where no unnecessarily duplicated or redundant data c. A separate physical implementation from the logical structure of data d. All of the above 8. Which of the following is NOT an advantage of using databases? a. Controlled redundancy b. Access control c. lower cost d. Multiple user interfaces 9. In ER diagram, entity set is represented by a. Triangle b. Rectangle c. Ellipse d. Double ellipse 10. Relational schema consists of list of attributes and their domain (a)true (b) False 11. The database manipulation language is a language that allows a. modification of the conceptual schema b. specification of updates and retrievals c. modification of the external schema d. the database structure to be modified Review Questions Part - A 1. What is DBMS? 2. Define database? 3. Give the application of DBMS? 4. What are the disadvantages of file processing system? 5. What are advantages of DBMS? 6. Define atomicity? 7. Define data abstraction? 8. Define data dictionary? 9. What is physical & logical data independence? 10. What are the different levels of data abstraction? 11. What is metadata? 12. Define instance and schema? 13. Define data model? 16

17 14. Define entity, attribute, and relationship? 15. Give the types of data model? 16. What is mapping cardinality? 17. Define DDL &DML? 18. What is query language and what are its types? 19. Difference between procedural & nonprocedural SQL? 20. What are the responsibilities of DBA? Part_B 1. Explain the Entity relationship model with suitable example 2. Explain the Relational data model with suitable example 17

Chapter 1: Introduction. Chapter 1: Introduction

Chapter 1: Introduction. Chapter 1: Introduction Chapter 1: Introduction Database System Concepts, 5th Ed. See www.db-book.com for conditions on re-use Chapter 1: Introduction Purpose of Database Systems View of Data Database Languages Relational Databases