Database Management Systems
MIT 22033Lesson 01 - Introduction
By S. Sabraz Nawaz
Introduction
• A database management system (DBMS) is a software package designed to create and maintain databases (examples?)
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Introducing the Database
• What is a database? A database is a collection of related data (University Database, Credit Card Processing Systems, Airline Reservation Systems, Banking System, etc.)
• A database is a shared, integrated computer structure that stores a collection of: End-user data, that is, raw facts of interest to the end user.
• Efficient data management typically requires the use of a computer database.
• Metadata, or data about data, through which the end-user data are integrated and managed.
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Database Management System (DBMS)
• A is a collection of programs that manages the database
structure and controls access to the data stored in the database.
In a sense, a database resembles a very well-organized
electronic filing cabinet in which powerful software, known as
a database management system, helps manage the cabinet’s
contents.
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DBMS: Role and Advantages
• The DBMS serves as the intermediary between the user and the database. The database structure itself is stored as a collection of files, and the only way to access the data in those files is through the DBMS.
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DBMS: Role
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DBMS: Role…
• The DBMS receives all application requests and translates them into the complex operations required to fulfill those requests. The DBMS hides much of the database’s internal complexity from the application programs and users.
• The application program might be written by a programmer using a programming language such as Visual Basic.NET, Java, or C#, or it might be created through a DBMS utility program.
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DBMS: Advantages
• Having a DBMS between the end user’s applications and the
database offers some important advantages. o First, the DBMS enables the data in the database to be shared among
multiple applications or users.
o Second, the DBMS integrates the many different users’ views of the
data into a single all-encompassing data repository.
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DBMS: Advantages - Improved data sharing
• The DBMS helps create an environment in which end users have better access to more and better-managed data. Such access makes it possible for end users to respond quickly to changes in their environment
• Concurrent accesses are scheduled by DBMS: users can think of the data as being accessed by one user at a time
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DBMS: Advantages - Improved data security
• The more users access the data, the greater the risks of data security breaches. Corporations invest considerable amounts of time, effort, and money to ensure that corporate data are used properly. A DBMS provides a framework for better enforcement of data privacy and security policies.
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DBMS: Advantages - Better data integration
• Wider access to well-managed data promotes an integrated view of the organization’s operations and a clearer view of the big picture. It becomes much easier to see how actions in one segment of the company affect other segments.
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DBMS: Advantages - Minimized data inconsistency
• Data inconsistency exists when different versions of the same data appear in different places.
• The probability of data inconsistency is greatly reduced in a properly designed database.
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DBMS: Advantages - Improved data access
• The DBMS makes it possible to produce quick answers to ad hoc queries.
• From a database perspective, a query is a specific request issued to the DBMS for data manipulation—for example, to read or update the data.
• Simply put, a query is a question, and an ad hoc query is a spur-of-the-moment question. The DBMS sends back an answer (called the query result set) to the application.
• Example?
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DBMS: Advantages - Improved decision making
• Better-managed data and improved data access make it possible to generate better-quality information, on which better decisions are based. The quality of the information generated depends on the quality of the underlying data.
• Data quality is a comprehensive approach to promoting the accuracy, validity, and timeliness of the data. While the DBMS does not guarantee data quality, it provides a framework to facilitate data quality initiatives.
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DBMS: Advantages - Increased end-user productivity
• The availability of data, combined with the tools that transform data into usable information, empowers end users to make quick, informed decisions that can make the difference between success and failure in the global economy.
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DBMS: Advantages- Reduced Application Development Time
• DBMS supports many functions common to applications that access the database
• These applications are likely to be more robust than applications developed from scratch because many important tasks are handled by DBMS instead of being implemented by the application
• Note: The advantages of using a DBMS are not limited to the few just listed. In fact, you will discover many more advantages as you learn more about the technical details of databases and their proper design.
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Types of Databases
• A DBMS can support many different types of databases. Databases can be classified according to the number of users, the database location(s), and the expected type and extent of use.
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Types of Databases: Number of Users
• A single-user database supports only one user at a time. In other words, if user A is using the database, users B and C must wait until user A is done. A single-user database that runs on a personal computer is called a desktop database.
• A multiuser database supports multiple users at the same time. When the multiuser database supports a relatively small number of users (usually fewer than 50) or a specific department within an organization, it is called a workgroup database.
• When the database is used by the entire organization and supports many users (more than 50, usually hundreds) across many departments, the database is known as an enterprise database.
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Types of Databases: Location
• A database that supports data located at a single site is called a centralized database.
• A database that supports data distributed across several different sites is called a distributed database.
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Types of Databases: Time and Usage
• Based on how DBMS are used and on the time sensitivity of the information gathered from them:o Operational Database (Transactional or production database)o Data warehouse
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Types of Databases: Time and Usage Operational Database
• Transactions such as product or service sales, payments, and supply purchases reflect critical day-to-day operations. Such transactions must be recorded accurately and immediately
• A database that is designed primarily to support a company’s day-to-day operations is classified as an operational database (sometimes referred to as a transactional or production database).
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Types of Databases: Time and Usage data warehouse
• A data warehouse focuses primarily on storing data used to generate information required to make tactical or strategic decisions. Such decisions typically require extensive “data massaging” (data manipulation) to extract information to formulate pricing decisions, sales forecasts, market positioning, and so on.
• Most decision support data are based on data obtained from operational databases over time and stored in data warehouses. Additionally, the data warehouse can store data derived from many sources. To make it easier to retrieve such data, the data warehouse structure is quite different from that of an operational or transactional database.
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Example of a database: University DB
• University database maintaining information concerning:o Studentso Courses, andoGradeso…
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An example of a database that stores students and their grades of followed courses
STUDENT Name StudentNumber Class Major
Smith 17 1 CSBrown 8 2 CS
COURSE CourseName CourseNumber CreditHouse Department
Intro to Computer Science CS 1310 4 CS
Data Structures CS 3320 4 CS
Discrete Mathematics MATH 2410 3 MATH
Database CS 3380 3 CS
SECTION Sectionaldentifier CourseNumber Semester Year Instructor
85 MATH 2410 Fall 98 King92 CS 1310 Fall 98 Anderson
102 CS 3320 Spring 99 Knuth112 MATH 2410 Fall 99 Chang119 CS 1310 Fall 99 Anderson
135 CS 3380 Fall 99 Stone
GRADE_REPORT StudentNumber Sectionaldentifier Grade 17 112 B
17 119 C8 85 A8 92 A8 102 B8 135 A
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Example: University DB (contd…)
• It shows the database structure and a few sample data.• It is organized as five files.
o The STUDENT file – data on each student,o The COURSE file – data on each course,o The SECTION file – data on each section of a course,o The GRADE_REPORT file – data on grades that students
receive in the various sections they have completed, ando The PREREQUISITE file – data on prerequisite of each course.
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Need for a DBMS
Traditional File System provided by the Operating System is insufficient to meet the requirements of enterprise applications
scenario: A company has a large collection (500 GB) of data on database. This data is accessed concurrently by several employees. Questions about the data must be answered quickly, changes made to the data by different users must be applied consistently, and access to certain parts of the data must be restricted.
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When NOT to use a DBMS
• High initial investment (DBMS is an expensive software package)
• Applications use small amounts of data
• Lack of resources (disk space, memory, etc.) to support a database
• Single-user applications
• Overhead for flexible querying, security, concurrent access & crash recovery is not required
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Describing & Storing Data in a DBMS
• A data model is a collection of high-level data description constructs used to model the application domain
• Data model hides the low-level storage details• Most commercial database systems are based on the
relational data model• It is easier to use a semantic data model to model an
application domain. A well-known semantic data model is the Entity Relationship (ER) Model
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Describing & Storing Data in a DBMS (cont.…)
• In relational data model, the main construct is a relation.• A relation has fields that belong to it which contain the name
& data type of each field • A description of data in terms of a data model is called the
schema.o Every relation has a schema, which describes the name of the
relation, name of each attribute (field or column), and the type of each column.
o e.g. Students(sid: string, name: string, login: string, age: integer, gpa: real)
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An example instance of the Students relation
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SID Name Login Age GPA
53666 SaNa [email protected] 33 3.8
53668 Kumar [email protected] 29 3.2
53670 Sanath [email protected] 41 3.9
Describing & Storing Data in a DBMS (cont.….)
• In addition to relational data model…o Hierarchical modelo Network modelo Object oriented modelo Object relational model
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Levels of Abstraction in a DBMS
• To illustrate the meaning of data abstraction, consider the example of automotive
design.
• A car designer begins by drawing the concept of the car that is to be produced. Next,
engineers design the details that help transfer the basic concept into a structure that can
be produced. Finally, the engineering drawings are translated into production
specifications to be used on the factory floor.
• As you can see, the process of producing the car begins at a high level of abstraction
and proceeds to an ever-increasing level of detail. The factory floor process cannot
proceed unless the engineering details are properly specified, and the engineering
details cannot exist without the basic conceptual framework created by the designer.
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Levels of Abstraction in a DBMS
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Levels of Abstraction in a DBMS
• DBMS is described at four levels of abstraction:
o External Model
o Conceptual Model
o Internal Model
o Physical Model
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Levels of Abstraction in a DBMS:
External Model• The external model is the end users’ view of the data environment. The term
end users refers to people who use the application programs to manipulate the data and generate information. End users usually operate in an environment in which an application has a specific business unit focus.
• Companies are generally divided into several business units, such as sales, finance, and marketing. Each business unit is subject to specific constraints and requirements, and each one uses a data subset of the overall data in the organization.
• Therefore, end users working within those business units view their data subsets as separate from or external to other units within the organization.
• A specific representation of an external view is known as an external schema.
• Because data are being modeled, ER diagrams will be used to represent the external views.
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Levels of Abstraction in a DBMS:
Conceptual Model• The conceptual model represents a global view of the entire database as viewed
by the entire organization. That is, the conceptual model integrates all external
views (entities, relationships, constraints, and processes) into a single global
view of the data in the enterprise.
• Also known as a conceptual schema, it is the basis for the identification and
high-level description of the main data objects (avoiding any database model–
specific details).
• The most widely used conceptual model is the ER model.
• Generally, the term logical design is used to refer to the task of creating a
conceptual data model that could be implemented in any DBMS.
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• Once a specific DBMS has been selected, the internal model maps the conceptual model to
the DBMS.
• The internal model is the representation of the database as “seen” by the DBMS. In other
words, the internal model requires the designer to match the conceptual model’s
characteristics and constraints to those of the selected implementation model.
• An internal schema depicts a specific representation of an internal model, using the
database constructs supported by the chosen database.
• Because the internal model depends on specific database software, it is said to be software-
dependent. Therefore, a change in the DBMS software requires that the internal model be
changed to fit the characteristics and requirements of the implementation database model.
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Levels of Abstraction in a DBMS:
Internal Model
• The physical model describes the way data are saved on storage media such as disks or tapes. The
physical model requires the definition of both the physical storage devices and the (physical) access
methods required to reach the data within those storage devices, making it both software- and
hardware- dependent.
• The storage structures used are dependent on the software (the DBMS and the operating system) and
on the type of storage devices that the computer can handle.
o Describes storage details
o Summarizes how the relations described in the conceptual schema are actually stored on
secondary storage devices such as disks and tapes
o Decide what file organizations used to store the relations
o Create indexes to speed up data retrieval operations
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Levels of Abstraction in a DBMS:
Physical Model
How does a DBMS do all this?• DBMS is a complex software package and the major components of a
DBMS are shown
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Queries In A DBMS
• With reference to a fictitious university database1. What is the name of the student with student ID
SEU/IS/98/MG/16?2. What is the average salary of lecturers who teach the
course with course ID MIT22033?3. How many students are enrolled in course MIT22033?4. Is there any student with a GPA less than 3.0 enrolled in
course CS564?• These questions involving the data stored in a DBMS are
called queries
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Queries In A DBMS…
• A DBMS provides a specialized language, called the query language in which queries can be posed
• Relational calculus is a formal query language based on mathematical logic
• Relational algebra is another formal query language, based on a collection of operators for manipulating relations, which is equivalent in power to the calculus
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Database Design Process
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Database Design Process
Requirements Analysis
Conceptual Database
Design
Logical Database
Design
Schema Refinement
Physical Database
Design
Security Design
Database design process can be divided into 6 major steps: (given in Raghu’s text book)
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Requirements Analysis
• This step answers the following question:
“What users want from the database?”
- what is going to be stored in the database- what applications are going to be built on top
the database- what are the most frequently asked queries
Requirements Analysis
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Requirements Analysis…
Result:
A well-written concise document enumerating the user’s requirements
Requirements Analysis
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Requirements Analysis…
For example: a library database…Data to be stored can be…• Record of all books in the library• Record of members of the library
o Studentso Facultyo Other members
• Record members’ borrowing information
Requirements Analysis
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Requirements Analysis…
Some applications on top of the database can be…
• Renewal service (may be on-line)
• Borrowing-Lending service• Resource reservation system
(may be on-line)• Resource request service
(may be on-line)
Requirements Analysis
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Conceptual Database Design
The information gathered in the requirements analysis phase is used to create a high-level description of the data in a conceptual data model. (Semantic Data Model, e.g. E-R Diagram )
Requirements Analysis
Conceptual Database
Design
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Logical Database Design
In this step, we determine the DBMS to implement the database & also the data model
We utilize the conceptual schema created in the previous step and convert it into a schema of a particular data model (e.g. Relational Database Schema)
Requirements Analysis
Conceptual Database
Design
Logical Database
Design
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Schema Refinement
The schema created by the logical database design phase is further refined for potential problems such as redundancies (e.g. Normalization)
Requirements Analysis
Conceptual Database Design
Logical Database Design
Schema Refinement
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Physical Database Design
In this step, performance criteria are taken into consideration and further enhancements to the schema & creation of indexes are considered
Requirements Analysis
Conceptual Database
Design
Logical Database
Design
Schema Refinement
Physical Database
Design
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Security Design
In this step, different user groups and their roles are identified. Appropriate levels of access are then provided to the data ensuring that users have access to only the necessary data.
Requirements Analysis
Conceptual Database
Design
Logical Database
Design
Schema Refinement
Physical Database
Design
Security Design
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The story is…
Requirements Analysis
Conceptual Database
Design
Logical Database
Design
Schema Refinement
Physical Database
Design
Security Design ER Diagram
Conceptual Schema or Logical Schema
Normalization B.Sc in MIT, SEUSL
Assignment #01
1. What is a data model? Describe the data models with example
2. Clearly explain the architecture of a DBMS
• Submission Deadline 31st December 2013
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Reference:Ramakrishnan, R., & Gehrke, J. (2003). Database management systems. Osborne/McGraw-Hill. (Pp. 03– 23)
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