Ice Objects

An Ice object is a conceptual entity, or abstraction. An Ice object can be characterized by the following points:

• An Ice object is an entity in the local or a remote address space that can respond to client requests.
• A single Ice object can be instantiated in a single server or, redundantly, in multiple servers. If an object has multiple simultaneous instantiations, it is still a single Ice object.
• Each Ice object has one or more interfaces. An interface is a collection of named operations that are supported by an object. Clients issue requests by invoking operations.
• An operation has zero or more parameters as well as a return value. Parameters and return values have a specific type. Parameters are named and have a direction: in-parameters are initialized by the client and passed to the server; out-parameters are initialized by the server and passed to the client. (The return value is simply a special out-parameter.)
• An Ice object has a distinguished interface, known as its main interface. In addition, an Ice object can provide zero or more alternate interfaces, known as facets. Clients can select among the facets of an object to choose the interface they want to work with.
• Each Ice object has a unique object identity. An object's identity is an identifying value that distinguishes the object from all other objects. The Ice object model assumes that object identities are globally unique, that is, no two objects within an Ice communication domain can have the same object identity.

In practice, you need not use object identities that are globally unique, such as UUIDs [14], only identities that do not clash with any other identity within your domain of interest. However, there are architectural advantages to using globally unique identifiers, which we explore in XREF.