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CS 2: chapter 2
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General Concepts
• Database definition– Organized collection of logically related data
• Data– Known facts– Types: text, graphics, images, sound, videos
• Database management system (DBMS)– Software package for defining and managing a
database
Introduction to DBMSData
Consists of raw facts, and when organized may be transformed into information
DatabaseA collection of related data organized to meet users needs
Database management system (DBMS)A group of programs that manipulate the database and provide an interface between the database and the user of the database. A Database Management System (DBMS) is a software system designed to store, manage, and facilitate access to databases.
Flat Files
Characteristics:• Data is stored as records in regular files• Records usually have a simple structure and fixed
number of fields• For fast access may support indexing of fields in the
records• No mechanisms for relating data between files• One needs special programs in order to access and
manipulate the data
Why Study Databases?
• Databases are useful– Many computing
applications deal with large amounts of information
– Database systems give a set of tools for storing, searching and managing this information
• Databases in CS– Databases are a ‘core topic’ in
computer science– Basic concepts and skills with
database systems are part of the skill set you will be assumed to have as a Computer science graduate
Database Basics
Traditional database organizes data in a hierarchy. A field is the smallest element. Fields are within a record. Records are organized in a data file. Database is a collection of data files.
File System DBMS
1 Less no. of files used 1 Large no. of files used
2 Doesn’t provide Security 2 Better Security, username and passward
3 Data redundancy is problemLoss of integrity-(accurate and consistent data)
3 Redundancy problem is solvedData is independenat
4 Data is isolated 4 Data is integrated
5 Data access takes lot of time 5 Less time
6 Concurrency control is not possibleSingle user system
6 Multiple user access data at same time
7 Little preliminary design 7 Vast permanent design
8 Transaction concept not usedEg:
8 Important in DBMSEg:
9 9
=Files vs. DBMS
• Must write special code for different queries• Must protect data from inconsistency due to multiple
concurrent users• Must manage crash recovery in some special-
purpose manner • Must provide good methods for access control
If we were to use files, we would have to :
Databases
• Web indexes• Library catalogues• Medical records• Bank accounts• Stock control• Personnel systems• Product catalogues• Telephone directories
• Train timetables• Airline bookings• Credit card details• Student records• Customer histories• Stock market prices• Discussion boards• and so on…
Database users• The people who interact with the database.
• End users – Use the database system to
achieve some goal -updating, inserting or modifying data from the database
• Application developers – Write application program
to allow end users to interface with the database system
• Database Administrator (DBA)– manages the database
system
• Database systems programmer– Writes the database
software itself
The people who interact with the database…
1. End users – updating, inserting or modifying data from the database
naïve users – only access the database based on their demand and access level, unaware of the DBMS, use predefined queries
sophisticated users – have complex requirements and queries, know the structure of the DBMS, engineers, scientists…
casual users – occasional users, need different data every time they come, use sophisticated queries…
Users …
Database Administrator - responsible to manage the database and the DBMS, authorize access, determine HW and SW resources.
Database Designer – identifies the data to be stored and design the structure of the database.
System Administrator – responsible for the entire computer system of the organization.
Why not text files, Spreadsheets..??
• Data integrity• Redundancy• Outdated data• Data size• Retrieval • Searching• Filtering• Protecting data from unauthorized use• Protecting data from becoming corrupt
Why Study Databases??• Shift from computation to information
– always true for corporate computing– Web made this point for personal computing– more and more true for scientific computing
• Need for DBMS has exploded in the last years– Corporate: retail swipe, “customer relationship mgmt”,
“supply chain mgmt”, “data warehouses”, etc.– Scientific: digital libraries, Human Genome project,
NASA Mission to Planet Earth, physical sensors, grid physics network
Why Use a DBMS?• Reduced application development time. • Data independence • Efficient data access.• Data integrity under updates.• Concurrent access• Recovery from crashes.• Security• Uniform data administration.
Databases make these people happy ...
• DBMS vendors, programmers– Oracle, IBM, MS, Sybase, …
• End users in many fields– Business, education, science, …
• DB application programmers– Build enterprise applications on top of DBMSs– Build web services that run off DBMSs
• Database administrators (DBAs)– Design logical/physical schemas– Handle security and authorization– Data availability, crash recovery – Database tuning as needs evolve
Levels of Abstraction
Physical Schema
Conceptual Schema
View 1 View 2 View 3
DB
Users
• Many views:– Views describe how users see the
data.
• conceptual (logical) schema– Conceptual schema defines logical
structure of DB and relationship between tables.
• physical schema:– Physical schema describes how
data is stored in a DB.
Data Independence
• Applications insulated from how data is structured and stored.
• Logical data independence: Protection from changes in logical structure of data.
• Physical data independence: Protection from changes in physical structure of data.
Physical Schema
Conceptual Schema
View 1 View 2 View 3
DB
Example: University Database
• Conceptual schema: – Students(sid: integer, name: string, login: string,
age: integer)– Courses(cid: string, cname: string, credits: integer) – Enrolled(sid: integer, cid:string, grade: string)
• Physical schema:– Relations stored as unordered files. – Index on first column of Students.
• External Schema (View): – Course_info
Data Entities, Attributes, and Keys
• Entity• A generalized class of people, places, or things (objects) for
which data are collected, stored, and maintained• E.g., Customer, Employee
• Attribute• A characteristic of an entity; something the entity is identified by• E.g., Customer name, Employee name
• Keys• A field or set of fields in a record that is used to identify the
record• E.g, A field or set of fields that uniquely identifies the record
Project Number Description Dept. Number
155 Payroll 257
498 Widgets 632
226 Sales manager 598
Dept. Number Dept. Name Manager SSN
257 Accounting 421-55-99993
632 Manufacturing 765-00-3192
598 Marketing 098-40-1370
SSN Last Name First Name Hire Date Dept. Number
005-10-6321 Johns Francine 10-7-65 257
549-77-1001 Buckley Bill 2-17-79 650
098-40-1370 Fiske Steven 1-5-85 598
Relation schema: A set of attributes is called a relation schema (or relation scheme). A relation schema is also known as table schemaIt is the logical definition of a table.
Relation schema defines what the name of the table is. This includes a set of column names, the data types associated with each column.
A database schema is the collection of relation schemas for a whole database. A database schema can be described a blueprint of a database that outlines the way data is organized into tables.
SQL statements are divided into two major categories: data definition language (DDL) and data manipulation language (DML). Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples: * CREATE - to create objects in the database* ALTER - alters the structure of the database* DROP - delete objects from the database* TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed* COMMENT - add comments to the data dictionary* RENAME - rename an object
Data Manipulation Language (DML) statements are used for managing data within schema objects.
Some examples: * SELECT - retrieve data from the a database* INSERT - insert data into a table* UPDATE - updates existing data within a table* DELETE - deletes all records from a table, the space for the records remain* MERGE - UPSERT operation (insert or update)* EXPLAIN PLAN - explain access path to data* LOCK TABLE - control concurrency
Data Control Language (DCL) statements. * GRANT - gives user's access privileges to database* REVOKE - withdraw access privileges given with the GRANT command
Transaction Control (TCL) statements are used to manage the changes made by DML statements. * COMMIT - save work done* SAVEPOINT - identify a point in a transaction to which you can later roll back* ROLLBACK - restore database to original since the last COMMIT
What are Data Models? Type of Data Models.
A model is a representation of reality, 'real world' objects and events, associations. It is an abstraction
Types:
Object Based Data ModelsRecord Based Data Models
Physical Data Models
Object Based Data Models
• Entity-Relationship • Object Oriented • Semantic • Functional
Record Based Logical Models
Record based logical models are used in describing data at the logical and view levels.
Each record type defines a fixed number of fields, or attributes, and each field is usually of a fixed length.
The three most widely accepted record based data models are: • Hierarchical Model • Network Model • Relational Model
Physical Data Models
Physical data models describe how data is stored in the computer, representing information such as record structures, record ordering, and access paths. There are not as many physical data models as logical data models, the most common one being the Unifying Model.
One mark question:1. State functions of DBA?2. State different data abstraction levels provided by DBMS?3. Define database system:4. Difference between file system & DBMS:5. What are views: Explain level of views.6. What is role of Naïve user in DBMS?7. Who all are dbms users?8. What is DML?9. What is DDL?10.What is DCL?11.What is TCL?12.Define Data Dictionary?13.Advantage of DBMS?14.Disadvantage of DBMS?15.Define Data Model?16.Types of DML?17.Differentiate procedural DML & Non-procedural DML:
Five mark question:
