Please enable JavaScript.

Coggle requires JavaScript to display documents.

CHAPTER 2: RELATIONAL DATA MODEL - Coggle Diagram

- - - - Airlines
      - Banking
      - Universities
      - Telecommunications
      - Others?
    - - Relation(table)
      - Tuple (row / record )
      - Attributte ( column / field )
      - Cardinality ( number of rows )
      - Degree ( number of columns )
      - Key ( Primary / Foreign / Candidate )
      - Domain ( a set of values allowed in an attribute )
      - Brianne Mith
  - - - RELATIONAL KEYS
        Primary Key
        
        candidate key selected to identify tuples (record) uniquely within relation.
        
        often a special ID attribute is used as the primary key Either {ID} or {First, Last} could be used as the primary key.
        
        ID is a better primary key since it is a single column, and it will always be unique.
        
        SARRAH AQILAH
        
        RELATIONAL KEYS
        NULL & Primary Keys
        
        Missing information can be represented using NULL.
        
        NULL indicates an unknown or missing value.
        
        Primary Keys cannot contain NULL values (entity integrity)
        
        ERITNEY MAJA
        
        RELATION KEY
        foreign key
        -an attribute whose values match primary key values in the related table
        -Foreign key are used to link data in two relations
        NURSYUHADDA AIN
- - - - RA: the general idea
        •It's an algebra, like the elementary algebra in math.
        •Math:
        -operands like 27.5 and x
        -operators like + and /
        -write expression describing the value you want
        • Relational algebra:
        -operands are tables
        -operands like "choose the rows that satisfy... "
        -Write expressions describing the table you want
        Victor Viets
        
        -Some operator are unary and some area binary -Operands are always relation the result will always be relation. -Example-> R1 op R2: result is a relation -> op R:result is a relation - You can compose an expression just like in arithmetic mathematics
        Mukhriz Danish
  - - - JOIN (⋈)
        
        Allows us to combine information from two or more tables.
        
        A refinement of the PRODUCT operation.
        
        By using EMPLOYEE and DEPARTMENT table, let see how to combine those tables by using JOIN.
        
        Example:
        EMPLOYEE ⋈ dept=dnr DEPARTMENT
        
        -puteri nadiatul-
        
        This is also known as INNER JOIN.
        -A join where the <condition> is the match (=) of the primary and foreign keys.
        R ⋈ <R.primary_key = S.foreign_key> S
        -puteri nadiatul-
        
        Combination of Unary and Join Operations
        
        Library Database
        (RELATION SCHEMA)
        
        Roselind
        
        Outer Joins
        
        extends the result of a simple join
        
        returns all rows that satisfy the join condition and returns some or all of those rows from one table for which no rows from the other satisfy the join condition
        
        There are 3 kinds of outer joins :
        
        Left Outer Join
        
        Right Outer Join
        
        Full Outer Join
        
        ~Josephine~
        
        Left Outer Joins
        
        all the tuples from the Left relation, R, are included in the resulting relation
        
        the S-attributes of the resulting relation are made NULL if the tuples in R does not have any matching tuple in the Right relation S
        
        ~Josephine~
        
        1 more item...
        
        Right Outer Join
        
        All the tuples from the Right relation, S, are included in the resulting relation.
        
        If there are tuple in S without any matching tuples in R, then the R-attributes of resulting relation are NULL
        
        Hadif
        
        Full Outer Join
        
        All the tuples from both participating relations are included in the resulting relatioon
        
        If there are no maatching tuples for both relations, their respective unmatched attributes are made NULL
        
        Andrew Kulleh
        
        1 more item...