> ## Documentation Index > Fetch the complete documentation index at: https://docs.metriport.com/llms.txt > Use this file to discover all available pages before exploring further. # MessageDefinition > Defines the characteristics of a message that can be shared between systems, including the type of event that initiates the message, the content to be transmitted and what response(s), if any, are permitted. ## Properties | Name | Required | Type | Description | | ------------------- | -------- | ------------------------------------------------------------------ | ------------------------------------------------------------ | | url | No | uri | Business Identifier for a given MessageDefinition | | identifier | No | [Identifier](/medical-api/fhir/data-types/identifier)\[] | Primary key for the message definition on a given server | | version | No | string | Business version of the message definition | | name | No | string | Name for this message definition (computer friendly) | | title | No | string | Name for this message definition (human friendly) | | replaces | No | canonical\[] | Takes the place of | | status | Yes | code | draft / active / retired / unknown | | experimental | No | boolean | For testing purposes, not real usage | | date | Yes | dateTime | Date last changed | | publisher | No | string | Name of the publisher (organization or individual) | | contact | No | [ContactDetail](/medical-api/fhir/data-types/contactdetail)\[] | Contact details for the publisher | | description | No | markdown | Natural language description of the message definition | | useContext | No | [UsageContext](/medical-api/fhir/data-types/usagecontext)\[] | The context that the content is intended to support | | jurisdiction | No | [CodeableConcept](/medical-api/fhir/data-types/codeableconcept)\[] | Intended jurisdiction for message definition (if applicable) | | purpose | No | markdown | Why this message definition is defined | | copyright | No | markdown | Use and/or publishing restrictions | | base | No | canonical | Definition this one is based on | | parent | No | canonical\[] | Protocol/workflow this is part of | | event\[x] | Yes | [Coding](/medical-api/fhir/data-types/coding), uri | Event code or link to the EventDefinition | | category | No | code | consequence / currency / notification | | focus | No | MessageDefinitionFocus | Resource(s) that are the subject of the event | | - id | No | string | Unique id for inter-element referencing | | - extension | No | [Extension](/medical-api/fhir/data-types/extension)\[] | Additional content defined by implementations | | - modifierExtension | No | [Extension](/medical-api/fhir/data-types/extension)\[] | Extensions that cannot be ignored even if unrecognized | | - code | Yes | code | Type of resource | | - profile | No | canonical | Profile that must be adhered to by focus | | - min | Yes | unsignedInt | Minimum number of focuses of this type | | - max | No | string | Maximum number of focuses of this type | | responseRequired | No | code | always / on-error / never / on-success | | allowedResponse | No | MessageDefinitionAllowedResponse | Responses to this message | | - id | No | string | Unique id for inter-element referencing | | - extension | No | [Extension](/medical-api/fhir/data-types/extension)\[] | Additional content defined by implementations | | - modifierExtension | No | [Extension](/medical-api/fhir/data-types/extension)\[] | Extensions that cannot be ignored even if unrecognized | | - message | Yes | canonical | Reference to allowed message definition response | | - situation | No | markdown | When should this response be used | | graph | No | canonical\[] | Canonical reference to a GraphDefinition | ## Search Parameters | Name | Type | Description | Expression | | --------------------- | --------- | ---------------------------------------------------------------------------------------- | ---------------------------------- | | context | token | A use context assigned to the message definition | MessageDefinition.useContext.value | | context-quantity | quantity | A quantity- or range-valued use context assigned to the message definition | MessageDefinition.useContext.value | | context-type | token | A type of use context assigned to the message definition | MessageDefinition.useContext.code | | date | date | The message definition publication date | MessageDefinition.date | | description | string | The description of the message definition | MessageDefinition.description | | jurisdiction | token | Intended jurisdiction for the message definition | MessageDefinition.jurisdiction | | name | string | Computationally friendly name of the message definition | MessageDefinition.name | | publisher | string | Name of the publisher of the message definition | MessageDefinition.publisher | | status | token | The current status of the message definition | MessageDefinition.status | | title | string | The human-friendly name of the message definition | MessageDefinition.title | | url | uri | The uri that identifies the message definition | MessageDefinition.url | | version | token | The business version of the message definition | MessageDefinition.version | | context-type-quantity | composite | A use context type and quantity- or range-based value assigned to the message definition | MessageDefinition.useContext | | context-type-value | composite | A use context type and value assigned to the message definition | MessageDefinition.useContext | | identifier | token | External identifier for the message definition | MessageDefinition.identifier | | category | token | The behavior associated with the message | MessageDefinition.category | | event | token | The event that triggers the message or link to the event definition. | MessageDefinition.event | | focus | token | A resource that is a permitted focus of the message | MessageDefinition.focus.code | | parent | reference | A resource that is the parent of the definition | MessageDefinition.parent | ## Inherited Properties | Name | Required | Type | Description | | ----------------- | -------- | ------------------------------------------------------ | ------------------------------------------------------ | | id | No | string | Logical id of this artifact | | meta | No | [Meta](/medical-api/fhir/data-types/meta) | Metadata about the resource | | implicitRules | No | uri | A set of rules under which this content was created | | language | No | code | Language of the resource content | | text | No | [Narrative](/medical-api/fhir/data-types/narrative) | Text summary of the resource, for human interpretation | | contained | No | Resource\[] | Contained, inline Resources | | extension | No | [Extension](/medical-api/fhir/data-types/extension)\[] | Additional content defined by implementations | | modifierExtension | No | [Extension](/medical-api/fhir/data-types/extension)\[] | Extensions that cannot be ignored | To view the FHIR specification for this resource, see [MessageDefinition](https://www.hl7.org/fhir/StructureDefinition/MessageDefinition).