Developing BPL Processes
Syntax Rules
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This chapter describes the syntax rules for referring to properties and for creating expressions within various BPL activities. It contains the following sections:

References to Message Properties
In activities within a BPL process, it may be necessary to refer to properties of the message. The rules for referring to a property are different depending on the kind of messages you are working with.
Literal Values
When you assign a value to a property, you often specify a literal value. Literal values are also sometimes suitable in other places, such as the value in a trace action.
A literal value is either of the following:
Important:
Due to the limitations of single-byte encoding format for HL7, the numeric value in character codes in literal strings placed in HL7 messages can be no higher than the decimal value 255 or hexadecimal x00FF.
XML Reserved Characters
Because BPL processes are saved as XML documents, you must use XML entities in the place of XML reserved characters:
To include this character... Use this XML entity...
> >
< &lt;
& &amp;
' &apos;
" &quot;
For example, to assign the value Joe’s "Good Time" Bar & Grill to a property, set Value equal to the following:
"Joe&apos;s &quot;Good Time&quot; Bar &amp; Grill"
This restriction does not apply inside <code> and <sql> activities, because Ensemble automatically wraps a CData block around the text that you enter into the editor. (In the XML standard, a CData block encloses text that should not be parsed as XML. Thus you can include reserved characters in that block.)
Separator Characters in Virtual Documents
In most of the virtual document formats, specific characters are used as separators between segments, between fields, between subfields, and so on. If you need to include any of these characters as literal text when you are setting a value in the message, you must instead use the applicable escape sequence, if any, for that document format.
These characters are documented in the applicable books. For details, see:
When XML Reserved Characters Are Also Separators
Numeric Character Codes
You can include decimal or hexadecimal representations of characters within literal strings.
The string &#n; represents a Unicode character when n is a decimal Unicode character number. One example is &#233; for the Latin e character with acute accent mark (é).
Alternatively, the string &#xh; represents a Unicode character when h is a hexadecimal Unicode character number. One example is &#x00BF; for the inverted question mark (¿).
Valid Expressions
When you assign a value to a property, you can specify an expression, in the language that you selected for the BPL process. You also use expressions in other places, such as the condition for an <if> activity, the value in a <trace> activity, statements in a <code> activity, and so on.
The following are all valid expressions:
Indirection
Ensemble supports indirection in values for the following BPL element-and-attribute combinations only:
The at sign symbol, @, is the indirection operator.
For example, the <call> element supports indirection in the values of the name or target attributes. The name identifies the call and may be referenced in a later <sync> element. The target is the configured name of the business operation or business process to which the request is being sent. Either of these strings can be a literal value:
<call name="Call" target="MyApp.MyOperation" async="1"> 
Or the @ indirection operator can be used to access the value of a context variable that contains the appropriate string:
<call name="@context.nextCallName" target="@context.nextBusinessHost" async="1"> 
This book describes @ indirection syntax in the documentation of each element that supports it: <call>, <sync>, and <transform>.
Important:
BPL and DTL are similar in many ways, but DTL does not support indirection.