DBMS: Database and Drawbacks of Using File Systems to Store Data

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Learning Objective

  • Define Database and Database management System

  • Describe the advantages of DBMS to file based system

  • Levels of Abstraction

  • Schema & Instance

  • Data Models

  • Relational Databases

Database

  • A Database is a logical, consistent, and organized collection of data that it can easily be accessed, managed, and updated.

  • Databases, also known as electronic databases are structured to provide the facility of creation, insertion, updating of the data efficiently and are stored in the form of a file or set of files, on the magnetic disk, tapes and another sort of secondary devices. Database mostly consists of the objects (tables), and tables include of the records and fields.

A Database is a logical

A Database is a Logical

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Database Management System (DBMS)

  • DBMS is a collection of programs that facilitates users to create and maintain a database.

  • A software package designed to store and manage databases.

Examples of 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

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.

  • 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 access needed for performance 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.

Levels of Abstraction

  • Physical level: It is the lowest level of abstraction. It describes how data are stored.

  • Logical level: It is the next higher level of abstraction. It describes what data are stored in the database and what the relationship among those data is.

  • View level: It is the highest level of data abstraction. It describes only part of the entire database. For example: User interacts with the system using the GUI and fill the required details, but the user doesn’t have any idea how the data is being used. So, the abstraction level is entirely high in View Level.

Instances & Schemas

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 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.

Data Models

A collection of tools for describing

Data

  • Data relationships

  • Data semantics

  • Data constraints

  • Relational model (we focus in this course)

  • Entity-Relationship data model (for database design)

  • Object-based data models (Object-oriented and Object-relational)

  • Semi-structured data model (XML)

Other older models:

Network model, Hierarchical model