Object and object-relational databases 1

Object databases vs. Object-relational databases Object databases Stores complex objects – Data + functions Uses classes and objects – As in object-oriented programming: Java, C#, etc. Some database management systems – Gemstone – Objectivity – Versant – ObjectStore Object-relational databases Relational DBMS with some object features Latest SQL standard (2008) includes some OO features Some database management systems – Oracle 2Object and object-relational databases

Object identity Every object in a object database must have a unique identity. – Called object identity (OID) – ID’s in relational databases must be unique within the table only. OID generated by DBMS OID must be immutable Literals (simple values) have no OID 3Object and object-relational databases

Complex type structures Atoms – Single value types, like string, int, etc. Struct aka. Tuple – Type generator: Heterogeneous members (different types) – Examples Struct Name Struct Student Collection aka. Multi-valued – Type generator: Homogeneous members (same type) – Set(T), List(T), bag(T), array(T), dictionary(T) Sub-types – You can define a sub-type of a struct by extending the struct. 4Object and object-relational databases

Collections Set(T) – Distinct members, duplicates not allowed – Java: Set Bag(T) – Duplicates members allowed – Java: Collection List(T) – Duplicates members allowed. Unlimited capacity – Ordered list It makes sense to ask for 1st element, 2nd element, etc. Order, is not necessarily sorting order – Java: List Array(T) – Like List(T), but Array(T) has a maximum size 5Object and object-relational databases

Example: Defining complex types 6Object and object-relational databases

Example: Defining complex types with operations 7Object and object-relational databases

Object-Relational databases Object-relational database – Add some object oriented features to an otherwise relational database Type constructors Object identity Operations Inheritance / sub-types – Tables creates using simple types + ”homemade” types Example Object-relational DBMS – Oracle has many OO features – Microsoft SQL Server has no OO features Object and object-relational databases 8

ODMG Object model and ODL ODMG =Object Data Management Group – Standard committee for Object oriented databases ODMG 1.0, 2.0, 3.0 Object model ODL = Object Definition Language ODL terms – Extent: Contains the persistent objects of a class – Key: One or more properties (attributes or relationships) – Factory object: similar to constructor in object- oriented programming Object and object-relational databases9

ODMG database schema Object and object-relational databases10

ODMG ODL example Object and object-relational databases11

Object Query Language (OQL) Defined by ODMG Writing queries for the ODMG object model Basic structure – Select … from … where As in ordinary SQL Example Select D.name from D in Departments where D.college = ’Engineering’ Departments is an ’extent’ D is a so-called iterator variable Object and object-relational databases12

Object-relational mapping (ORM) Alternative to object databases and object- relational databases ORM programming technique to convert data between object-oriented programming languages and relational databases. – A virtual object database Some frameworks – Hibernate for Java NHibernate for Microsoft.NET – ADO.NET Entity Framework for Microsoft.NET 13Object and object-relational databases