About Message Definitions
Data messages coming into Tracking Server must have a format that matches a message definition in order to be processed.
Message Definitions
Data messages convey event information throughout Tracking Server. The format of these messages is defined in Tracking Server Manager on the Message Definitions tab. Message definitions are at the core of how event data moves. Without a valid message definition, Tracking Server will not process event data. The Message Definitions tab provides a list of all message definitions defined for Tracking Server.
From the Message Definitions tab you can add, edit, and delete message definitions. The ability to import and export message definitions is also provided. Once a message definition has been created, it can be exported to a file. The file can then be put on another Tracking Server machine and imported via the Message Definitions tab. When message definitions are added, deleted, or changed, a status message is sent out to all connected clients of Tracking Server. Tracking services and actions are based on message definitions. If a message definition is deleted, any associated tracking services or actions are also deleted.
Message definitions describe the fields and field types of the event data coming in or going out of Tracking Server. Each message definition must be uniquely named and assigned a unique identifier. Other information in a message definition includes the time zone and coordinate system of the data. The time zone should be set to the time zone of where the event data is originating. The time zone information is required to be able to adjust the data to a local time when viewing it in a client application. Similarly, the coordinate system for the event data must be set when creating a message definition to ensure correct projection of the data when viewing it in a client application.
There are two types of message definitions: observations and objects. Observation message definitions are ones that must include date and time as one of the fields. Geometry or shape information, as well as other attribute information, may also be part of an observation message. Object message definitions can either be created by the user or derived from a geodatabase.
Object messages contain the static attribute information that does not change over time. The importance of the designation between observation and object message definitions will become more apparent when you begin to create tracking services.
Certain information in a message definition is mandatory. First, all message definitions must have a unique name. Also, there must be one field that is designated to be the Track or Event ID field. The value in this field is usually a unique identifier field for the data. If one of the fields in the message definition is a shape field (point, polyline, or polygon), a coordinate system must be specified. All observation message definitions must include a date/time stamp field.
There are specific criteria for naming message definitions. The names must be composed of alphabetic or numeric characters and may contain “_”. No spaces are allowed within the name. Also, the names are restricted based on SQL naming standards. This is a necessary restriction to support logging to SQL databases. For a complete list of restricted words, refer to Appendix C: Reserved Words.
The primary reason for message definitions is to define event data. Fields and field types are used to specifically define the data. Field names follow the same restrictions as described above for message definition names.
All field names within a message definition must be unique. As for the field types, there are many different possibilities for describing the data. The following types are supported by message definitions:
- Boolean: 1 byte with values of 1 or 0
- Date: Standard Windows representation of date and time
- Double: Base 10 floating-point number
- Integer: Base 10 integer number
- Point: ESRI geometry type
- Polygon: ESRI geometry type
- Polyline: ESRI geometry type
- String: String with unspecified length
- String 512: String with length up to 512 bytes
- String 256: String with length up to 256 bytes
- String 64: String with length up to 64 bytes
- String 32: String with length up to 32 bytes
- String 16: String with length up to 16 bytes
- String 8: String with length up to 8 bytes
- String 4: String with length up to 4 bytes
- String 2: String with length up to 2 bytes
- String 1: String with length up to 1 byte
- Timestamp: Supports oledatetime and string
Another feature of message definitions is the ability to add metadata to each message as Tracking Server processes it. Metadata is a text string that can contain information regarding the source of the data, accuracy, latency, and so forth.