Conceptual database design components

Conceptual database design components .

Entiti objek dimana data dikumpul, seperti manusia , tempat objek fizikal sebenar atau hanya satu konsep.

Contoh : kejadian individu entity

Enternal entity: satu entity yang dihunakan untuk bertukar-tukar data, tetapi tidak disimpan di dalam pengkalan data

Attribute: fakta unit tentang kira0kira entity tertentu.

Relationship: an association / persatuan antara entity

Business rule : dasar , prosedur atau standart yang organisasi gunakan dan yang menentukan kawalan tertentu ke atas dat,n sering dilaksanakan dalam pengkalan data sebagai karangan

Relationship

Maximum cardinality :  bilangan maksimum , contoh satu entity boleh dikaitkan

Transferable : hubungan yang boleh dipindah milik jika ibu bapa yang mungkin berubah dari masa ke semasa .

Conditional in one direction : means that a corresponding record may or not be found on the optional side of the relationship

Conditional in both direction: means that corresponding record may or not be found on the optional side of the relationship

Mandatory in one direction: means that a corresponding must exist on the mandatory side of the relationship

Mandatory in both directions: : means that corresponding record must be found on both sides of the relationship

One-to-many: indicates that are record in one table may be related to many (usually0+) records in another table.

Many-to-many: this can be thought of as one-to-many relationship that goes in both directions; many-to-many relationships are not natively supported in relational databases, but there are ways to convert them into something that can be handled.

Intersection data: data that is associated with two related entities in a many-to-many relationship, and which only makes sense when associated with both related entities; intersection data can beplaced (mapped) into a separate table to help relational databases handle the many –to-many relationship

Recursive: refers to relationships between instances of the same entity type

ENTITY-RELATIONSHIP DIAGRAMS

Graphical data model

Entities are represented by rectangles

Unique identifier (primary key) located in rectangle at top of the entity rectangle it is a unique identifier for

  

EMPLOYEE ID

      Last Name

      FirstName

      HourlyRate

       Position

Logical database design components

·         Table: a 2-D logical structure like a grid where each row contains attributes about a single instance of the entity type the table represents , and each column represents a particular attribute

o   Entities are sometimes split into two tables

o   Different entities are sometimes merged into a single table (rare)

o   Entities are usually named using a plural , while tables are named in the

Column: the smallest named unit of data in a database

·         Columns must be given a data type.

·         Data types help the database store data efficiently

·         Data type restrict attribute values to the correct data type and provides a set of behaviors consistent with the specified data type (such as addition, subtraction. Etc. for numbers

·         Unfortunately, different vendors support differing zoos of data types.

Constraints: rules that restrictallowable data values

      Primary key: one or more colums that uniquely identify a particular row in a table

Ø  The constraint is that duplicate values are not allowed in the primary key column(s) of a table

Ø  Primary keys are usually implemented as an index

Ø  An index speeds up searches

·         Foreign key: afield on the many-side side of a one-to-many relationship that  uniquely identifies one row in another table (usually by using the primary key in the latter table)

·         Referential constraints:

Ø  Can check for parent record when inserting new child record (using the child record’s foreign key to check for a matching parent record

Ø  Don’t allow modification of child record’s foreign key if the new value is not reprensented by an istance in the parent table

Ø  Can delete all matching child records when a parent tecord is deleted

·         Integrity constraints: used to make sure field (atrtribute) values that are invalid are not allowed

Ø  May check for a range of values, or specific valid values

Ø  May check for NOT  NULL

·         TRIGGERS: A TRIGGER IS APROGRAM STORED IN THE DATABASE THAT RUNS WHEN A SPECIFIC EVENT HAPPENS. Triggers can be used to validate data (among other things).

Surrogate key: a key used to replace what would be the natural key for an entity

Views : refers to the way different esers may see the same database differently

·         Views are stored queries (virtual tables)

·         Views can hide colums (cleaner , more secure)

·         Views can hide tables (cleaner, more secure)

·         Views can hide complex operations such as joins

·         Views may improve query performance