2.3 messages

OMG CORBA IDL

Messages are not explicitly identified in the CORBA Specification.

ODMG

See 2.1 operations.

EXPRESS

No notion of messages.

Open Distributed Processing

Generally, messages are used in object interactions, but not explicitlyidentified. Rather, only the notion of interaction is identified.

Management Information Model

Not applicable.

SQL3

See 2.2 requests and 2.4 specification of behavioral semantics

Matisse

Messages are part of the Matisse metamodel and are used to invoke operations(methods).

C++

See 2.2 requests and 2.4 specification of behavioral semantics

Smalltalk

A Smalltalk message is a request to an object instance to perform anoperation. A message expression consists of a receiver, selector (messagename), and potentially some arguments. The selector must be mapped to amethod of the same name, encapsulated in the receiver object's class hierarchy.The arguments, if any, are used by the method to perform its operation.Message syntax occurs in one of three forms: unary, binary, and keyword.

Unary Messages have no arguments.

Example - Inventory deltaFromYesterday
In this case, Inventory is a variable identifying the receiver object,and deltaFromYesterday is the selector.

Binary Messages have one argument.

Example - 2+3
In this case, the object "2" is the receiver, "+" isthe selector, and "3" is the argument.

Keyword Messages have one or more arguments. The selector in keywordmessages is composed of a keyword ahead of each argument. Keywords in messagesare identified by a trailing colon.

Example with two keywords - CorporateBudget updateWith: $3000 on: 'Travel'
In this case, CorporateBudget is a variable identifying the receiver object,and updateWith: on: is the selector.

Eiffel

Not applicable.

Cecil

All computation in Cecil is accomplished by sending messages to objects.Method lookup in response to a message is constrained by argument specializersdefined for the methods (see 2.5 methods). Informally, a messageis considered as being sent to all its argument objects. When a messageis sent, the system finds all methods with the same name and number ofarguments as the message. The system then eliminates from considerationthose methods whose argument specializers are too restrictive to applyto the actual parameters passed in the call (if no methods are applicableafter this step, a "message not understood" error is reported).Of the remaining applicable methods, the system locates the one whose argumentspecializers are most specific, and invokes that method to respond to themessage. If no single method is most specific, a "message ambiguous"error is reported (i.e., Cecil does not attempt to resolve ambiguity itself).[Cha92]

SELF

See entry under 2. Objects.

System Object Model (SOM)

Messages are not explicitly identified in SOM.

Analysis and Design Methods

SA: There is no explicit concept of messages.Instances generate events for themselves or other instances. Events carryparameters.

CA: See 2.2 requests. "...eachMessage Connection represents values sent within the context of a particularservice need, and a response received as a result."

RA: There is no explicit concept of messages.Instances generate events for themselves or other instances. Events carryparameters.

JA: "The dynamics in an object-orientedmodel is created through the dynamic relations, by means of objects [instances]sending stimuli to other objects. We denote by the concept stimulus theevent when an object communicates with another object. In a programmingcontext, the word 'message' is often used instead, but in order to avoidthe message-semantic, we use the stimulus concept."

WD: "A message consists of the nameof an operation and any required arguments."

MD: The term 'message' is not used. Routinesare applied to objects. The routines may have parameters.

EA: "The most common type of interactionamong objects is communication." "Two objects communicate whenone object sends a message to another object. ...[M]essages are tangibleor intangible objects transmitted in an interaction."

FA: "A system operation is alwaysinvoked by an [external] agent, not an object; the analysis phase is notconcerned with internal messaging between objects."

FD: "Message passing is a directedpoint-to-point communication, and is realized as a function or method call.""A message may involve bi-directional data flow when the invocationof a method returns a value." "When a message is sent to an objectit results in the invocation of a method. The method call completes beforecontrol is returned to the caller. If the invoked method also sends messagesto other objects, the methods that are invoked must all complete beforethe initial invocation completes." "The object interaction graphdefines the sequence of messages that occur between a collection of objectsto realize a particular operation."

OA: "Messages ... are a more restrictedcase of requests. A message supplies only one object in its request foran operation along with any number of object parameters. A request is notlimited to one object it requests for an operation."

BD: "The terms message, method,and operation are usually interchangeable." See 2.1 operations.

HA: "Message are the triggers foractivating services. Messages are instantaneous in time." "Oncea message is received, the appropriate service is activated."

NA: "Message[:] A feature call.""[W]e switch freely between the message passing metaphor and the featurecall metaphor (objects invoking operations on each other) ..." "[S]endinga message to an object, calling a class feature, or invoking an operationon an object ... always mean the same thing."

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