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The Meta Object

The meta object contains meta-information describing the event: when it was created, where it came from, its type et cetera. The meta object contains the same members regardless of meta.type1, with the caveat that certain members are optional and the tendency to use them may vary with event type.

Meta Members

meta.id

Type: String
Format: UUID
Required: Yes
Description: The unique identity of the event, generated at event creation.

meta.type

Type: String
Format: An event type name
Required: Yes
Description: The type of event. This field is required by the recipient of the event, as each event type has a specific meaning and a specific set of members in the data and links objects.

meta.version

Type: String
Format: Semantic Versioning 2.0.0
Required: Yes
Description: The version of the event type. This field is required by the recipient of the event to interpret the contents. Please see Versioning for more information.

meta.time

Type: Integer
Format: Milliseconds since epoch.
Required: Yes
Description: The event creation timestamp.

meta.tags

Type: String[]
Format: Free text
Required: No
Description: Any tags or keywords associated with the events, for searchability purposes.

meta.source

Type: Object
Format:
Required: No
Description: A description of the source of the event. This object is primarily for traceability purposes, and while optional, some form of identification of the source is HIGHLY RECOMMENDED. It offers multiple methods of identifying the source of the event, techniques which may be select from based on the technology domain and needs in any particular use case.

meta.source.domainId

Type: String
Format: Free text
Required: No
Description: Identifies the domain that produced an event. A domain is an infrastructure topological concept, which may or may not corresponds to an organization or product structures. A good example would be Java packages notation, ex. com.mycompany.product.component or mycompany.site.division. Also, keep in mind that all names are more or less prone to change. Particularly, it is recommended to avoid organizational names or site names, as organizations tend to be volatile and development is easily relocated. Relatively speaking, product and component names tend to be more stable and are therefore encouraged, while code names may be an option. You need to decide what is the most sensible option in your case.

meta.source.host

Type: String
Format: Hostname
Required: No
Description: The hostname of the event sender.

meta.source.name

Type: String
Format: Free text
Required: No
Description: The name of the event sender.

meta.source.serializer

Type: Object
Format:
Required: No
Description: The GAV coordinates of the serializer software used to construct the event.

meta.source.serializer.groupId

Type: String
Format: groupId
Required: Yes
Description: The groupId of the serializer software.

meta.source.serializer.artifactId

Type: String
Format: artifactId
Required: Yes
Description: The artifactId of the serializer software.

meta.source.serializer.version

Type: String
Format: version
Required: Yes
Description: The version of the serializer software.

meta.source.uri

Type: String
Format: URI
Required: No
Description: The URI of, related to or describing the event sender.

meta.security

Type: Object
Format:
Required: No
Description: An optional object for enclosing security related information, particularly supporting data integrity. See Security for further information.

meta.security.sdm

Type: Object
Format:
Required: No
Description: An optional object for properties supporting the Strong Distribution Model. Note that this only addressed the integrity of the Eiffel event, not its confidentiality or availability.

meta.security.sdm.authorIdentity

Type: String
Format:
Required: Yes
Description: The identity of the author of the event. This property is intended to enable the recipient to look up the appropriate public key for decrypting the digest and thereby verifying author identity and data integrity. The format of the author identity varies depending on the key infrastructure solution used. Note that this requires the presence of a Trusted Authority (TA) which the recipient can query for the correct public key. The identity and location of the TA must never be included in the event itself, as this would compromise the security of the solution.

meta.security.sdm.encryptedDigest

Type: String
Format:
Required: Yes
Description: The encrypted digest. The cryptographic hash function and the decryption algorithm to use, similarly to the Trusted Authority (TA), must be known to the recipient. Note that the digest of the entire event is affected by the value of this property. For this reason the input to the hash function SHALL be the entire event unaltered in all parts except for this property, which SHALL be replaced by an empty string.

   

 

1: Event types are versioned independently from one another. There are three important consequences of this. First, any change to meta requires all events to be updated. Second, any schema of a specific version of an event must also include the meta object – specifically as it is defined for that version of the event. Third, consumers should be prepared to receive events of varying meta contents. The exception to this are the meta.type and meta.version fields, which are always assumed to be present change.