Download ppt - DATA MODELING AND DATABASE DESIGN Part 3

DATA MODELING AND DATA MODELING AND DATABASE DESIGNDATABASE DESIGN

Part 3Part 3

Objectives

• Translate Logical to Physical design

• Steps for converting (mapping) Resolved ERD to set of Table Instance Charts

• Table Instance Charts symbols.

• Some mapping examples

Database Design -from Logical to Physical

• Map entities and attributes to tables and columns respectively.

• Naming conventions should be consistent.

• Consider primary, unique and foreign keys

and check constraints as well

• Additional requirements– Design the indexes

– Establish view definitions

– Plan the physical storage space

Steps to convert your Resolved ERD to TIC set

• Map ENTITIES to TABLES

• Map ATTRIBUTES to COLUMNS

• Map * to NOT NULL constraints

• Map UIDs to PRIMARY KEY constraints

• Map (#) Secondary UIDs to NOT NULL and UNIQUE Constraints

• Map RELATIONSHIPS to FKs

Table Instance Chart Symbols

• PK - Primary Key

• FK - Foreign Key

• FK1, FK1 - Composite Foreign Keys

• FK1, FK2 - Two foreign keys related to two separate tables

• NN - Not Null

• U - Unique

• U1, U1 - Two columns unique in combination with each other

• U1, U2 - Two unique (and indepenent) columns

Column nameKey typeNulls/UniqueFK tableFKcolumnDatatypeMax lengthValidate

emp_no

PK,FK

EMPLOYEEemp_no

NUM7

position

NN

CHAR25

salary

NN

NUM11,2

Comm

NUM4,2

Creating a TIC: ExampleCreate a Table Instance Chart (TIC) from the Logical Schema (Resolved ERD)

EMPLOYEE_NEW_FORCE TableEMPLOYEE_NEW_FORCE Table

Columns

Keys

Reference

< 10000 < 1

Steps for creating TIC1: Map Entities to Tables

• Create a frame for each TIC– Table name

– Column names

– Key types

– Not Null and Unique references

– Foreign key information

– Column datatype and maximum length

_ Validation (Check)

– Sample data

• Put the table name at the top of the chart.

Step 2: Map the Attributes to Columns

• Map each attribute from the entity to a column name in the table.

• Mandatory columns get a NN constraint

• Add sample data for each column (usually three rows)

• Do not use SQL reserved words for column names.

Step 3: Map the Unique Identifiers to Primary Keys

• Map the UID of the entity as the primary key in the table.

• Do NOT mark it as NN and U

• If there is an alternate UID, label it as NN and U,but choose only one for a PK.

• Add a FK column for each UID that is through a relationship (over UID bar)

Step 4: Map Relationships to Foreign Keys

• For One-to-Many relationships– Take the PK at the One end and create a

column under same or different name in the other table at the Many end.

– Mark it as a FK.

• For mandatory relationships, be sure to label the NN reference.

Step 4: Map Relationships to Foreign Keys --- continued

• For One-to-One relationships, label the U reference.– If the relationship is optional in both

directions, place the FK in the table at either end of the relationship.

– If the relationship is mandatory, place the unique FK in the table at the mandatory end.

• For mandatory relationships, be sure to label the NN reference.

MAPPING: Example

EMPLOYEE_NEW_FORCE ACTIVITY

EMPLOYEE_ACTIVITY

* per_diem_rate

# emp_no* positiono job_description* salaryo commission

# activity_id* descriptiono start_dateo end_date* internal

requires

for

performs

performedby

Entities to tablesEMPLOYEE_NEW_FORCE ACTIVITY

EMPLOYEE_ACTIVITY

Attributes to ColumnsColumn Name id description start_date end_date internal

KeyType Nulls/Uniques

FK RefTableFK ColumnDatatypeMAX LengthValidation

ACTIVITY

UID to PK and * to NOT NULL



ACTIVITY

PK

NN NN

Column Name id description start_date end_date internal

If Entity on Many side, then add FK Column



ACTIVITY

PK

NN NN


NN

We do NOT have here a FK Column !

Validation (Check) on Columns with Limits



ACTIVITY

PK

NN NN


>= sysdate {Y,N}

NN

LINK - INTERSECTION ENTITIES

EMPLOYEE_ACTIVITY

forfor

PK and NN

Column Name emp_no activity_id per_diem_rate

KeyType PK PK

Nulls/Uniques NN

FK RefTable

FK refColumn DatatypeMAXLength

EMPLOYEE_ACTIVITY

Foreign KeysColumn Name emp_no activity_id per_diem_rateKeyType PK, FK1 PK, FK2

Nulls/Uniques NN

FK Ref . EMPLOYEE_ ACTIVITY table NEW_FORCE

FK refColumn emp_no activity_id Datatype Number Number NumberMAXLength 6 6 7,2

EMPLOYEE_ACTIVITY

Foreign Key Mapping Rules

• Map the Relationship to a foreign key.

• One to One optional in both directions - take the PK from either table and make it a FK in the other table.

• One to One mandatory in one direction, take the PK from the optional end and make it a FK in the entity at the mandatory end.

• One to Many - Take the PK at the one end and make it a FK in the entity at the many end.

• Do not forget to label mandatory relations with NN