Message model objects

An introduction to the objects that make up a message model. Message model objects are defined by XML Schema 1.0, except for Message which is an IBM® Integration Bus extension to XML Schema.

Message: A message describes the structure and content of a set of data that is exchanged between applications that send and receive the data. A message is a special complex element.
Simple element: A simple element describes one or more named data fields in a message. It is based on a simple type (for example, string, integer or float). A simple element can repeat, and it can define a default or a fixed value.
Simple type: A simple type describes a class of data within a message. It describes the type of data (for example, string, integer or float) and it can have value constraints which place limits on the values of any simple elements based on that simple type.
Complex element: A complex element describes a named complex structure within the message. The content of a complex element is defined by a complex type. A complex element can repeat.
Complex type: A complex type describes a complex structure within a message. It contains elements (simple or complex), attributes (if the data is XML), and groups that are organized into a tree-like hierarchy.
Group: A group describes a list of elements with information about how those elements can appear in a message. Groups can be ordered (sequence), unordered (all), or selective (choice). A group can repeat.
Attribute: An attribute describes an XML attribute. Attributes are similar to simple elements, but they require special treatment when used with XML messages. In messages that are not XML messages, attributes are not used.

Global and local objects

Most objects in the message model can be either global or local. A global object must have a unique name, which is used to refer to the object from one or more places in the message model. Local objects are defined and used in only one place in the message model.

Make objects local unless they must be used in more than one place. This reduces the probability of name clashes among the global objects in the message model, and makes the message set easier to work with.

Properties of message model objects

All message model objects have properties. The properties fall into three categories:

Logical: The logical properties of an object are defined by XML Schema. They relate to the format-independent description of the object called the 'logical model'. Logical properties describe what data the object contains without saying anything about how it is written down.
Physical: If the message model is for a data format that is not XML, additional physical properties are provided for an object that describe how the object is written down. These properties control the parsing and writing of the object. If the message model is a DFDL schema, then the properties are defined by the DFDL 1.0 specification. If the message model is in a message set, then the properties are an IBM proprietary set that is understood by the MRM domain and parser.
Documentation: This field is present for all message model objects. It provides a standard place for any description of the object that you might require. Text entered here does not affect the processing of messages in any way.