Adbms 15 object data management group
- 1. Advance Database Management Systems : 15 Object Data Management Group (ODMG) Prof Neeraj Bhargava Vaibhav Khanna Department of Computer Science School of Engineering and Systems Sciences Maharshi Dayanand Saraswati University Ajmer
- 2. Slide 21- 2 Objectives • Discuss the importance of standards (e.g., portability, interoperability) • Introduce Object Data Management Group (ODMG): object model, object definition language (ODL), object query language (OQL) • Present ODMG object binding to programming languages (e.g., C++) • Present Object Database Conceptual Design
- 3. Slide 21- 3 The Object Model of ODMG • Provides a standard model for object databases • Supports object definition via ODL • Supports object querying via OQL • Supports a variety of data types and type constructors
- 4. Slide 21- 4 ODMG Objects and Literals • The basic building blocks of the object model are – Objects – Literals • An object has four characteristics 1. Identifier: unique system-wide identifier 2. Name: unique within a particular database and/or program; it is optional 3. Lifetime: persistent vs. transient 4. Structure: specifies how object is constructed by the type constructor and whether it is an atomic object
- 5. Slide 21- 5 ODMG Literals • A literal has a current value but not an identifier • Three types of literals 1. atomic: predefined; basic data type values (e.g., short, float, boolean, char) 2. structured: values that are constructed by type constructors (e.g., date, struct variables) 3. collection: a collection (e.g., array) of values or objects
- 6. Slide 21- 6 ODMG Interface Definition: An Example • Note: interface is ODMG’s keyword for class/type interface Date:Object { enum weekday{sun,mon,tue,wed,thu,fri,sat}; enum Month{jan,feb,mar,…,dec}; unsigned short year(); unsigned short month(); unsigned short day(); … boolean is_equal(in Date other_date); };
- 7. Slide 21- 7 Built-in Interfaces for Collection Objects • A collection object inherits the basic collection interface, for example: – cardinality() – is_empty() – insert_element() – remove_element() – contains_element() – create_iterator()
- 8. Slide 21- 8 Collection Types • Collection objects are further specialized into types like a set, list, bag, array, and dictionary • Each collection type may provide additional interfaces, for example, a set provides: – create_union() – create_difference() – is_subset_of( – is_superset_of() – is_proper_subset_of()
- 9. Slide 21- 9 Object Inheritance Hierarchy
- 10. Slide 21- 10 Atomic Objects • Atomic objects are user-defined objects and are defined via keyword class • An example: class Employee (extent all_emplyees key ssn) { attribute string name; attribute string ssn; attribute short age; relationship Dept works_for; void reassign(in string new_name); }
- 11. Slide 21- 11 Class Extents • An ODMG object can have an extent defined via a class declaration – Each extent is given a name and will contain all persistent objects of that class – For Employee class, for example, the extent is called all_employees – This is similar to creating an object of type Set<Employee> and making it persistent
- 12. Slide 21- 12 Class Key • A class key consists of one or more unique attributes • For the Employee class, the key is ssn – Thus each employee is expected to have a unique ssn • Keys can be composite, e.g., – (key dnumber, dname)
- 13. Slide 21- 13 Object Factory • An object factory is used to generate individual objects via its operations • An example: interface ObjectFactory { Object new (); }; • new() returns new objects with an object_id • One can create their own factory interface by inheriting the above interface
- 14. Slide 21- 14 Interface and Class Definition • ODMG supports two concepts for specifying object types: – Interface – Class • There are similarities and differences between interfaces and classes • Both have behaviors (operations) and state (attributes and relationships)
- 15. Slide 21- 15 ODMG Interface • An interface is a specification of the abstract behavior of an object type – State properties of an interface (i.e., its attributes and relationships) cannot be inherited from – Objects cannot be instantiated from an interface
- 16. Slide 21- 16 ODMG Class • A class is a specification of abstract behavior and state of an object type – A class is Instantiable – Supports “extends” inheritance to allow both state and behavior inheritance among classes – Multiple inheritance via “extends” is not allowed
- 17. Assignment • What do you understand by collection object. Give example of some interfaces related to collection objects. • Explain the concept of interface and class on OODBMS