Following are three levels of data 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…

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An entity set that doesn’t have sufficient attributes to form a primary key is referred to as a weak entity set. The member of a weak entity set is known as a subordinate entity. Weak entity set does not have a primary key, but we need a mean to differentiate among all those entries in the entity set that depend on one particular strong entity set.

You have to use Structured Query Language (SQL) to communicate with the RDBMS. Using queries of SQL, we can give the input to the database and then after processing of the queries database will provide us the required output. To communicate with an RDBMS (Relational Database Management System), you typically use Structured Query Language (SQL). SQL allows you to interact with the database by performing tasks such as querying data, inserting new records, updating existing records, and deleting records. Additionally,…

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What are the three levels of data abstraction? Following are three levels of data 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…

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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. Fields…

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Data Definition Language (DDL) is a standard for commands which defines the different structures in a database. Most commonly DDL statements are CREATE, ALTER, and DROP. These commands are used for updating data into the database. DDL, or Data Definition Language, is a set of commands used to define and manage the structure of a database and its objects. These commands enable users to create, modify, and delete database objects such as tables, indexes, views, and schemas. Examples of DDL…

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An attribute refers to a database component. It is used to describe the property of an entity. An attribute can be defined as the characteristics of the entity. Entities can be uniquely identified using the attributes. Attributes represent the instances in the row of the database. For example: If a student is an entity in the table then age will be the attribute of that student.

Shared lock: Shared lock is required for reading a data item. In the shared lock, many transactions may hold a lock on the same data item. When more than one transaction is allowed to read the data items then that is known as the shared lock. Exclusive lock: When any transaction is about to perform the write operation, then the lock on the data item is an exclusive lock. Because, if we allow more than one transaction then that will…

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What do you mean by extension and intension? Extension: The Extension is the number of tuples present in a table at any instance. It changes as the tuples are created, updated and destroyed. The actual data in the database change quite frequently. So, the data in the database at a particular moment in time is known as extension or database state or snapshot. It is time dependent. Intension: Intension is also known as Data Schema and defined as the description of the…

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The collection of database and DBMS software together is known as a database system. Through the database system, we can perform many activities such as- The data can be stored in the database with ease, and there are no issues of data redundancy and data inconsistency. The data will be extracted from the database using DBMS software whenever required. So, the combination of database and DBMS software enables one to store, retrieve and access data with considerate accuracy and security.