Date post: | 22-Apr-2015 |
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Technology |
Upload: | ahmed-magdy |
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Object Role Modeling
Prepared by Ahmed Magdy Ezzeldin
Outline
What & Why ORM?
ORM Building Blocks
Example
ORM Process
ORM Symbol Glossary
Summary
What & Why ORM?
Object Role Modeling (ORM) is a powerful method for designing and querying database models at the conceptual level, where the application is described in non-technical terms.
1. Communicating models with your team2. Communicating and validating models with your client3. Great brainstorming tool
In practice, ORM data models often capture more business rules, and are easier to validate and evolve than data models in other approaches.
ORM Building Blocks
Object Types- Entity Types (map directly to an ER Entity)- Value Types (map directly to ER attributes)
Facts- Predicates: {0} is enrolled in {1}- Roles: {0} and {1}
Constraints- Like uniqueness constraint
Example
The Student named Ahmed is enrolled in the Course named Math
Entity Types: Student, Course Value Types: Ahmed, Math
We have 3 Facts (predicates) with 2 roles each:- Student is named Ahmed- Course is named Math- Student is enrolled in Course
ORM Process
To model any application using ORM we need to follow these steps starting from the requirements provided by the domain expert:
1. Transform information examples into facts
2. Draw the Entity & value types
3. Add Fact types and assign roles
4. Add constraints
Description Symbol Example
Entity Type Student, course, song, band
Value Type Student name, course name, song title, band name
Fact with 2 roles (Predicate with 2 arities)
Student is enrolled in course
Uniqueness Constraint (has one) the first role is unique ti the second role.
Each student has at most 1 namebut there may be 2 students who have the same name
1:1 both roles are unique to each other
Every student has at most one name and there are no 2 students with the same name.
m:n Many to many Every student may be enrolled in many courses and each course may have many students.
ORM Symbol Glossary
Value
Entity
Summary
ORM can be changed to ER.
ORM can easily be changed to UML.
ORM is rich as it captures more business details by capturing facts and constraints.
Questions
Thank you
Questions
???