Introduction
A virtual document is a kind of message that InterSystems IRIS® data platform parses only partially. To understand the purpose of virtual documents, it is useful to examine production messages a little more closely. Every production message consists of two parts:
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The message header contains the data needed to route the message within InterSystems IRIS. The message header is always the same type of object. This is a persistent object, meaning that it is stored within a table in the InterSystems IRIS database.
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The message body contains the message data. For standard messages, the message body is a persistent object. For virtual documents, the message body is implemented in a different way, as explained below.
An object represents each piece of data as a separate property. This is convenient in that any value in the object is easy to access. When writing code, you simply reference a class property by name to get its value.
For EDI (Electronic Data Interchange) formats, this approach becomes unwieldy and unnecessary. The approach is unwieldy because a large number of properties (possibly hundreds) would be required, and the process of creating an instance of the object can be slow. The standard approach is unnecessary because many applications use only a small number of the fields actually available in the document.
To address these issues, InterSystems IRIS provides an alternative type of message body called a virtual document. A virtual document allows you to send raw document content as a body of a production message, without creating objects to hold the contents of the document as a formal set of properties. The data in the virtual document is stored directly in an internal-use global, for greater processing speed.
The virtual document approach is also useful for XML documents (which can also be handled as standard messages).
