Database Concepts
Class 12 · Computer Science
4 ideas in Class 12 Computer Science, explained in plain words, with games and quizzes to practise.
File System and Its Limits
Part of: From files to databases
A file is a container that stores data on a computer, and programs read and write it. When related data spreads across files, the same names repeat, which is redundancy, and copies can disagree, which is inconsistency. Files also stay isolated with no links, depend on fixed formats, and share access poorly.
Why it matters. Manual registers and scattered files lose data and disagree with each other. Learners who name each limitation see why schools and shops outgrow files.
Key words
- File
- : A container that stores data on a computer.
- Redundancy
- : The same data repeated in different places.
- Inconsistency
- : Copies of the same data that disagree.
- Isolation
- : Related files kept with no links between them.
- Data Dependence
- : Programs breaking when a file format changes.
Try it in two minutes
- Write one pupil name in two notebooks with a spelling change.
- Ask which copy is correct and how you would know.
- Count the hand entries for a class over a month.
Try at home. Ask your child to find one repeated name in two home lists and fix the mismatch.
DBMS and Its Ideas
Part of: From files to databases
A database management system is software that creates and runs databases where related tables link through common columns. The schema is the design, the instance is the data snapshot at a moment, and metadata describes the design. Users ask questions with queries and change data with insertion, deletion and update steps.
Why it matters. One linked store ends repeats and disagreements and serves many users at once. Learners who grasp schema, instance and queries can plan real stores for schools and shops.
Key words
- DBMS
- : Software that creates and manages databases.
- Schema
- : The design of tables, columns and links.
- Instance
- : The data snapshot at a given moment.
- Query
- : A request for information from the database.
- Constraint
- : A rule limiting what a column may hold.
Try it in two minutes
- Sketch two linked tables sharing one common column.
- Add one row and call the new snapshot by its name.
- Ask a question the linked tables can answer together.
Try at home. Ask your child to design two linked tables for a home library.
Relations Tables and Terms
Part of: Relational model and keys
In the relational model every table is a relation with rows called tuples and columns called attributes. The degree counts the attributes and the cardinality counts the rows. Each column draws values from one domain, holds single atomic values, and unknown entries use the special mark NULL.
Why it matters. These terms let teams describe any table exactly and set correct rules. Learners who count degree and cardinality read any database diagram with ease.
Key words
- Relation
- : A table of related rows and columns.
- Tuple
- : One row of the relation.
- Attribute
- : One column of the relation.
- Degree
- : The count of attributes in the relation.
- Cardinality
- : The count of tuples in the relation.
Try it in two minutes
- Draw a small book table with five columns and six rows.
- Count the columns and name the degree.
- Count the rows and name the cardinality.
Try at home. Ask your child to find the degree and cardinality of one home table.
Keys That Link Tables
Part of: Relational model and keys
Keys keep every row reachable. Candidate keys are columns with distinct values, the designer picks one as the primary key and the rest stay alternate. When no single column suffices, two columns together form a composite key. A foreign key in one table points to the primary key of another, linking them.
Why it matters. Right keys stop duplicates and join tables correctly for bills, attendance and loans. Learners who pick keys well build stores that stay clean as they grow.
Key words
- Candidate Key
- : A column with distinct values fit to identify rows.
- Primary Key
- : The chosen column that uniquely identifies rows.
- Alternate Key
- : A candidate key not chosen as primary.
- Composite Key
- : Two or more columns together as the primary key.
- Foreign Key
- : A column pointing to the primary key of another table.
Try it in two minutes
- List columns with distinct values in a table.
- Crown one as primary and name the alternates.
- Link two tables through a shared column.
Try at home. Ask your child to pick a primary key for a home book table.
What your child will practise
- DBMS and Its Ideas: Jungle Quick Fire (Quick Fire)
- File System and Its Limits: Candy Quick Fire (Quick Fire)
- File System and Its Limits: Space Puzzle (Clue Puzzle)
- Keys That Link Tables: Desert Quick Fire (Quick Fire)
- Relations Tables and Terms: Jungle Puzzle (Clue Puzzle)
- Quiz: DBMS and Its Ideas (8 questions)
- Quiz: File System and Its Limits (8 questions)
- Quiz: Keys That Link Tables (8 questions)
- Quiz: Relations Tables and Terms (8 questions)