Define ODMG object model. What is object query language (OQL)?

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 ODMG object model

  •  It is an object data management Group, (ODMG) The ODMG object model is the data model upon which the object definition language (ODL) and object query language (OQL) are based.
  •  It is meant to provide a standard data model for object databases, just as SQL describes a standard data model for relational databases. 
  • It also provides a standard terminology in a field where the same terms were sometimes used to describe different concepts. 

Object query language (OQL) 

  • OQL is an SQL-like declarative language that provides a rich environment for efficient querying of database objects, including high-level primitives for object sets and structures.
  • OQL also includes object extensions for object identity, complex objects, path expressions, operation invocation, and inheritance. OQL's queries can invoke operations in ODMG language bindings, and OQL may be embedded in an ODMG language binding.
  • The object query language OQL is the query language proposed for the ODMG object model. It is designed to work closely with the programming languages for which an ODMG binding is defined, such as C++, Smalltalk, and Java. Hence, an OQL query embedded into one of these programming languages can return objects that match the type system of that language. 
  • The OQL syntax for queries is similar to the syntax of the relational standard query language SQL, with additional features for ODMG concepts, such as object identity, complex objects, operations, inheritance, polymorphism, and relationships.


Below is an example of an OQL query

SELECT  c.address

FROM    Persons p,

p.children c

WHERE p.address.street="Main Street" AND

COUNT (p.children) >= 2 AND

c.address.city != p.address.city;


SELECT=> can construct new objects and arbitrary structures.

FROM=> tuple variables can range over any collection; may have subqueries.

WHERE=> pretty much the same as in SQL.



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