Domain Prefixes

Overview

This page details the various domain prefixes used in Appian. Domain prefixes appear before the identifying name of certain functions, rules, data, etc. Between the prefix and name is an exclamation mark !, also referred to as a 'bang'.

Domain prefixes serve a couple of purposes:

• Reference design objects and functions: In the appropriate context, domain prefixes are used to reference a design object or a function.
• Invoke properties: In the appropriate context, domain prefixes are used to invoke a particular property.
• Prevent name collisions: If functions, rules, or other properties are identically named, the domain prefix will define what Appian uses.

Domain prefixes are used anywhere you can create an expression. However, certain prefixes are only used in certain contexts.

After entering a domain prefix in an expression, a type ahead will begin to suggest the best matched function, object, or data point.

Function prefixes

There are two function domain prefixes in Appian: fn! and a!. When you type the a! or fn! domain into an expression and followed by a character, type ahead will suggest functions that map to the domain and character you entered. Always use the a! domain when you need to call various system, smart service, and connector functions as well as interface components.

Unlike the a! domain, the fn! domain is not required to call a related function, unless you are referencing a function within another function. For example, the all() function allows you to evaluate whether a given function or rule is true or false for each item in a list. As shown in the expression below, the fn function is required to reference the isnull() function within the all() function.

all(fn!isnull, {10, null, 30})

Object prefixes

Design objects also have a domain prefix that allows you to directly or indirectly reference a design object or invoke object properties. The following table list the various design objects with their prefixes.

Design Object	Domain Prefix	Reference Type	Use Case
Constants	cons!	Indirect	Use this domain to indirectly reference a design object. See Call a Constant from an Expression for more information.
Data Types	type!	Direct	Use this domain to reference an Appian data type or custom data types. See Construction Data Type Values for examples on how to use this prefix. See Data prefixes for information on which data prefixes to use to invoke stored data values in an expression.
Decisions	rule!	Indirect	Use this domain to indirectly reference an expression rule, an interface, a decision, and an integration. See Call a decision from another expression for more information.
Expression Rules	rule!	Indirect	Use this domain to indirectly reference an expression rule, an interface, a decision, and an integration. See Call an expression rule from another expression for more information.
Integrations	rule!	Indirect	Use this domain to indirectly reference an expression rule, an interface, a decision, and an integration. See Call an integration to query data for more information.
Interfaces	rule!	Indirect	Use this domain to indirectly reference an expression rule, an interface, a decision, and an integration. See Interfaces as rules for more information.
Record Type Object	recordType!	Direct	Use this domain to reference a record object type and any properties of the record type like fields, actions, filters, and relationships. See Reference a record type and its properties for more information.

Direct and indirect object references

Direct object references are used to call an object directly into an expression or function. These references use the appropriate domain prefix for the design object followed by the name of the design object. If the object has rule inputs or properties, the direct object reference allows you to pass the inputs or properties into the expression as parameters.

Indirect object references are used for design objects that you cannot call directly into an expression. This reference type is helpful for calling objects that vary between environments and objects that are referenced in multiple design objects. For example, if you want to assign a security group to multiple design objects and the group's access rights vary across environments, you could use a single constant to reference the security group and call it in each environment.

Data prefixes

You can use data prefixes to reference data types or invoke stored data values. Certain data prefixes are specific to a single object type while others can be used in multiple object types.

Multiple object prefixes

The following data prefix can be used in multiple object types in Appian:

Name	Prefix	Description	Level	Example
Rule Inputs	ri!	Invokes rule inputs from rule-based objects, like expression rules, interfaces, and decisions.

Single object prefix

The following prefixes can only be invoked in certain cases: within an object's expression editors (like process models or record types).

Process only prefixes

Process models have several out-of-the-box domain prefixes that you can use in expression editors in the Process Modeler. You can also use some of these prefixes when editing task report data columns. Learn more about process-only prefixes.

Record only prefixes

Record types have three domain prefixes that can be used to retrieve certain record variables, fields, and properties.

Name	Prefix	Description
Record Variables	rv!	This domain prefix is always followed by identifier or record. This domain allows you to reference record values within the record type object itself: To reference a record's ID, use rv!identifier. To reference the data within a specific field in a record, use rv!record and combine it with a reference to the field using the recordType! domain. For example: rv!record[recordType!Employee.fields.firstName]
Record Fields	rf!	This prefix is not supported for record types created or updated in 20.3 and beyond.
Record Properties	rp!	This prefix is not supported for record types created or updated in 20.3 and beyond.
Record Service Properties	rsp!	Exclusively used in legacy expression-backed records created with Appian 19.4 and earlier to handle paging, searching, and filtering. The rsp! domain is no longer required to configure these record fields. See default filters using expressions and user filters for record types that use a web service for more information on the new, simpler configuration experience.

Web API only prefixes

Name	Prefix	Description
Web API properties	http!	Use in Web APIs to expose certain http properties when someone calls that web API.

Test prefixes

Name	Prefix	Description
Test cases	test!output	Use in expression rules to create test assertions based on the test's output.

Function-specific prefixes

Within certain functions, properties of that function can be called by using the following prefixes:

Name	Prefix	Description
Local Variables	local	Through the a!localVariables() function designers can create local variables and call those local variables using the local! prefix.
Function Variables	fv!	Used within certain functions and interface components. The available function variables will be listed in the inline documentation.
Save Value	save!	Used within a!save() function.

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