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Program composition that supports buildingobject-oriented systems as compositions of subjects,extending systems by composing them with new subjects, andintegrating systems by composing them with one another(perhaps with glue or adapter subjects).The flexibility of subject composition introduces novelopportunities for developing and modularising object-orientedprograms. Subject-oriented programming-in-the-large involvesdividing a system into subjects and writing rules to composethem correctly. It complements object-oriented programming,solving a number of problems that arise when OOP is used todevelop large systems or suites of interoperating orintegrated applications.IBM subject-oriented programming(http://research.ibm.com/sop/).