Each object stores different real-world values. This allows you to create software components that are modular, maintainable, and reusable. For more information, see Chapter  9 . A collection is an ordered group of elements, all of the same type. Each element has a unique subscript that determines its position in the collection.
Collections work like the arrays found in most third-generation programming languages.
They can store instances of an object type and, conversely, can be attributes of an object type. Also, collections can be passed as parameters. So, you can use them to move columns of data into and out of database tables or between client-side applications and stored subprograms. For more information, see Chapter  4 . And, they allow efficient, random, piece-wise access to the data.