Context nodes and expression syntax

A report configuration will contain instructions about what values to include from the target Class Library definition. These instructions come in form of Value expressions. To understand these expressions, it is beneficial to have a basic understanding of the Class Library node graph. Think of the Class Library as a collection of connected nodes, where a simplified view might look something like this:

The diagram above can be explained as:

• A Class Library has a collection of pre-defined properties

• A Class Library has a collection of Functional Classes

• The collection of Functional Classes might contain one or more Functional Class definitions

• A Functional Class definition has a collection of pre-defined Properties

• A Functional Class definition has a collection of permissible Attributes

• The collection of permissible Attributes might contain one or more permissible Attribute definitions

• A permissible Attribute has a collection of pre-defined Properties

• A Functional Class definition might have Extensions

• The Functional Class Extensions might contain extensions from one or more extension Namespaces

• An extension Namespaces might contain one or more extension Nodes

• An extension Node might contain one or more Properties

• An extension Node might contain one or more Child Nodes

• A Class Library has a collection of Attribute Classes

• The collection of Attribute Classes might contain one or more Attribute Class definitions

• An Attribute Class definition has a collection of pre-defined Properties

• A Class Library definition might have Extensions

• The Class Library Extensions might contain extensions from one or more extension Namespaces

• An extension Namespaces might contain one or more extension Nodes

• An extension Node might contain one or more Properties

The diagram shows a small selection of the full Class Library model in AVEVA ISM, just to give you an idea of how the model works, as a background to understand Value expressions in a Permissible Grid configuration. The node graph for Document, Physical and General classes are like the one showed for Functional classes in the diagram.

An example of a node value expression might look something like this:

<Columns headerStyle="TagHeader">

<Column geicl:id="ClassId" header="Functional Class Id" value="./@id" />

<Column geicl:id="ClassName" header="Functional Class Name" value="./@name"/>

</Columns>

During output of a Permissible Grid, AVEVA ISM iterates over the nodes in the target Class Library model (i.e. the Attribute Classes, the Classes of specified concept and the Permissible Attributes of those Classes). A Value expressions in the configuration is then interpreted in the context of the current node. The syntax example above is an excerpt from the configuration on how to render properties from the Classes, down the left-hand side of the Permissible Grid, hence these expressions are resolved in the context of a Class:

• The "." (dot) at the start of the expression symbolizes the context, which in this case is the current Class

• The "/" (forward slash) instructs to follow one of the connecting lines (4, 5 or 8 in the diagram above)

• The "@" (at sign) instructs that the line to follow is for a property (i.e. line 4 in the diagram above)

• The name following the "@" is the name of the property to pick (i.e. "id" and "name" respectively)

The result of these expressions is the value of property id, and name respectively, of the current Class.

Be aware that even though the diagram above shows extensions for a Class and the ClassLibrary node only, all nodes in the AVEVA ISM Class Library model can potentially contain an Extensions node. The diagram above is simplified for brevity.