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Database Systems - Introduction to Database Systems
This presentation highlights on introductions and basics of Database and Database Management Systems (DBMS). Topics covered are Basic Definitions of Databases, Types of Databases and Database Applications, What a DBMS Facilitates and Other Functionalities, Main Characteristics of the Database Approach, Advantages of Using the Database Approach, Database Users, Database Users – Actors on the Scene, Database End Users, When not to use a DBMS, Data Models, Categories of Data Models, Database Schema versus Database State, Three-Schema Architecture, Data Independence, DBMS Languages, and DBMS Interfaces.
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Database Systems - Introduction to Database Systems
- 1.Lecture 1Introduction toDatabase System1
- 2.Basic Definitions■ Data:■Known facts that can be recorded and have an implicit meaning.■ Database:■ A collection of related data which is logically coherent and is builtfor a specific purpose.■ Mini-world:■ Some part of the real world about which data is stored in adatabase. For example, student grades and transcripts at auniversity.■ Database Management System (DBMS):■ A software package/system to facilitate the creation andmaintenance of a computerized database.■ Database system:■ The DBMS software together with the data itself. Sometimes, theapplications are also included.2
- 3.Example of aSimple DatabaseFig 1: University Database that stores student information, course enrolments and grades3
- 4.Types of Databasesand DatabaseApplications■ Traditional applications:■ Numeric and textual databases■ More recent applications:■ Multimedia databases■ Geographic Information Systems (GIS)■ Biological and genome databases■ Data warehouses■ Mobile databases■ Real-time and active databases4
- 5.Managing DataThere aretwo approaches to manage data There are twoapproaches to manage data:● File-based approach: An approach that utilizes a collectionof application programs which performs services toend-users (e.g. Reports). Each program defines andmanages its own data.● Database approach: An approach that data is collectedand manipulated using specific software called DatabaseManagement System, and many programs share this data.5
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- 8.A simplified architecturefor adatabase system8
- 9.What a DBMSFacilitates■ Define a particular database in terms of its data types,structures, and constraints■ Construct or load the initial database contents on asecondary storage medium■ Manipulating the database:■ Retrieval: Querying, generating reports■ Modification: Insertions, deletions and updates to itscontent■ Accessing the database through Web applications■ Processing and sharing by a set of concurrent users andapplication programs – yet, keeping all data valid andconsistent9
- 10.Other DBMS Functionalities■DBMS may additionally provide:■ Protection or security measures to preventunauthorized access■ “Active” processing to take internal actions on data■ Presentation and visualization of data■ Maintenance of the database and associatedprograms over the lifetime of the databaseapplication10
- 11.Main Characteristics oftheDatabase Approach■ Self-describing nature of a database system:■ A DBMS catalog stores the description of a particulardatabase (e.g. data structures, types, and constraints)■ The description is called meta-data.■ This allows the DBMS software to work with differentdatabase applications.■ Insulation between programs and data:■ Called program-data independence.■ Allows changing data structures and storage organizationwithout having to change the DBMS access programs11
- 12.Main Characteristics oftheDatabase Approach (continued)■ Data abstraction:■ A data model is used to hide storage details andpresent the users with a conceptual view of thedatabase.■ Support of multiple views of the data:■ Each user may see a different view of thedatabase, which describes only the data ofinterest to that user.12
- 13.Main Characteristics oftheDatabase Approach (continued)■ Sharing of data and multi-user transaction processing:■ Allowing a set of concurrent users to retrieve from and toupdate the database.■ Concurrency control within the DBMS guarantees that eachtransaction is correctly executed or aborted■ Recovery subsystem ensures each completed transactionhas its effect permanently recorded in the database or iftransaction fails then the database rolls back to the lastvalid state.■ OLTP (Online Transaction Processing) is a major part ofdatabase applications; allows hundreds of concurrenttransactions to execute per second.13
- 14.Advantages of UsingtheDatabase Approach■ Controlling redundancy in data storage and indevelopment and maintenance efforts.■ Sharing of data among multiple users.■ Restricting unauthorized access to data. Only theDBA staff uses privileged commands andfacilities.■ Providing storage structures (e.g. indexes) forefficient query processing.14
- 15.Advantages of UsingtheDatabase Approach (continued)■ Providing optimization of queries for efficientprocessing■ Providing backup and recovery services■ Providing multiple interfaces to different classesof users■ Representing complex relationships among data■ Enforcing integrity constraints on the database■ Drawing inferences and actions from the storeddata using deductive and active rules andtriggers15
- 16.Database Users■ Usersmay be divided into■ Those who actually use and control the databasecontent, and those who design, develop andmaintain database applications (called “Actors onthe Scene”), and■ Those who design and develop the DBMSsoftware and related tools, and the computersystems operators (called “Workers Behind theScene”).16
- 17.Database Users –Actors on theScene■ Actors on the scene (4 types)■ Database administrators■ Responsible for authorizing access to the database, forcoordinating and monitoring its use, acquiring software andhardware resources, controlling its use and monitoringefficiency of operations.■ Database designers■ Responsible to define the content, the structure, theconstraints, and functions or transactions against thedatabase. They must communicate with the end-users andunderstand their needs.■ Software Engineers■ Responsible for implementing the database and its associatedapplications using a dbms and other programming languagesand tools.17
- 18.Database End Users■Actors on the scene (continued)■ End-users: They use the data for queries, reports andsome of them update the database content. End-users canbe categorized into:■ Casual: access database occasionally when needed■ Naïve or parametric: they make up a large section of theend-user population, e.g mobile app and social mediausers, constantly update and access the database.■ Sophisticated: business analysts, scientists, engineers,others thoroughly familiar with the system capabilities.■ Stand-alone: Mostly maintain personal databases usingready-to-use packaged applications.18
- 19.When not touse a DBMS■ Main inhibitors (costs) of using a DBMS:■ High initial investment and possible need for additionalhardware■ Overhead for providing generality, security, concurrencycontrol, recovery, and integrity functions■ When a DBMS may be unnecessary:■ If the database and applications are simple, well defined,and not expected to change■ If access to data by multiple users is not required■ When a DBMS may be infeasible■ In embedded systems where a general-purpose DBMS maynot fit in available storage19
- 20.When not touse a DBMS■ When no DBMS may suffice:■ If there are stringent real-time requirementsthat may not be met because of DBMSoverhead (e.g., telephone switching systems)■ If the database system is not able to handle thecomplexity of data because of modelinglimitations (e.g., in complex genome and proteindatabases)■ If the database users need special operations notsupported by the DBMS (e.g., GIS andlocation-based services).20
- 21.Data ModelsA setof concepts to describe the structure of a database, theoperations for manipulating these structures, and certainconstraints that the database should obey.21
- 22.Categories of DataModels■ Conceptual (high-level, semantic) data models:■ Provide concepts that are close to the way many usersperceive data.■ (Also called entity-based or object-based data models.)■ Physical (low-level, internal) data models:■ Provide concepts that describe details of how data is storedin the computer. These are usually specified in an ad-hocmanner through DBMS design and administration manuals■ Implementation (representational) data models:■ Provide concepts that fall between the above two, used bymany commercial DBMS implementations (e.g. relationaldata models used in many commercial systems).■ Self-Describing Data Models:■ Combine the description of data with the data values.Examples include XML, key-value stores and some NOSQLsystems. 22
- 23.Database Schema versusDatabaseState■ Database Schema:■ The description of a database■ Includes descriptions of the database structure,data types, and the constraints on the database.■ Schema Diagram:■ An illustrative display of (most aspects of) adatabase schema.■ The database schema changes very infrequently■ Schema is also called intension.23
- 24.Example of aDatabase Schema24
- 25.Database Schema versusDatabaseState■ Database State:■ The actual data stored in a database at aparticular moment in time. This includes thecollection of all the data in the database.■ Also called database instance (or occurrence orsnapshot).■ The database state changes every time the database isupdated.■ State is also called extension.25
- 26.Example of adatabase state26
- 27.Three-Schema Architecture■ Proposedto support DBMS characteristics of:■ Program-data independence.■ Support of multiple views of the data.■ Not explicitly used in commercial DBMS products,but has been useful in explaining databasesystem organization27
- 28.Three-Schema Architecture■ DefinesDBMS schemas at three levels:■ Internal schema at the internal level to describe physicalstorage structures and access paths (e.g indexes).■ Typically uses a physical data model.■ Conceptual schema at the conceptual level to describe thestructure and constraints for the whole database for acommunity of users.■ Uses a conceptual or an implementation data model.■ External schemas at the external level to describe thevarious user views.■ Usually uses the same data model as the conceptual schema.28
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- 30.Data IndependenceThe abilityto change the schema at one level withoutimpacting the schema at the next higher level. Two types ofdata independence:■ Logical Data Independence:■ The capacity to change the conceptual schema without having tochange the external schemas and their associated applicationprograms.■ Example: adding a new column that is not shown in the app orchanging the datatype which does not change the external view.■ Physical Data Independence:■ The capacity to change the internal schema without having tochange the conceptual schema.■ For example, the internal schema may be changed when certainfile structures are reorganized or new indexes are created toimprove database performance30
- 31.DBMS Languages■ DataDefinition Language (DDL): Used to define databaseschemas. The ddl statement is used to identify the descriptionof a schema construct and store the schema description in theDBMS catalog. Creating/Deleting a table, Adding columns,Changing data types are examples that require DDLstatements.■ Data Manipulation Language (DML): Used to manipulatedata by inserting, deleting, updating and retrieving data. DMLcommands can be embedded in a general-purposeprogramming language such as Java. Two types of DML:high-level/non-procedural and low-level/procedural.31
- 32.DBMS Interfaces■ Stand-alonequery language interfaces■ Example: Entering SQL queries at the DBMS interactiveSQL interface (e.g. SQL*Plus in ORACLE)■ Programmer interfaces for embedding DML in programminglanguages■ User-friendly interfaces■ Menu-based, forms-based, graphics-based, naturallanguage interfaces, etc.■ Mobile Interfaces:interfaces allowing users to performtransactions using mobile apps■ Parametric interfaces, e.g., bank tellers using function keys.■ Interfaces for the DBA.32