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The free text data type can convey any data that is primarily meant to be shown to human beings for interpretation. Free text can be any kind of text, whether unformatted or formatted written language or other multi media data.
For text/plain media defines the character encoding if different from default encoding. Defaults to the encoding used for ST.
Indicates that the raw byte data is compressed and what compression algorithm was used.
Contains the free text data as raw bytes.
The cryptographically strong checksum algorithm SHA-1 (Standard Hash Algorithm-1) is currently the industry standard. It has superseded the MD5 algorithm only a couple of years ago, when certain flaws in the security of MD5 were discovered. Currently the SHA-1 hash algorithm is the default and mandatory only choice for the integrity check algorithm. However, there is no assurance that SHA-1 will not be superseded as quickly as MD5 was superseded.
Default: SHA-1
Rationale: The ic_algorithm is recognized now so that HL7 is prepared to accommodate the change to another algorithm should such algorithm supersede SHA-1.
The ED.integrity_check attribute is a cryptographically strong checksum (SHA-1 algorithm by default) that is calculated over the binary data block. The system resolving a data reference can calculate the checksum over the received data and can thus validate whether the data received is actually the same data that the HL7 message has referred to earlier.
Rationale: Since the data referenced is only coupled to the message by a telecommunication address, the coupling between message and referred data is quite loose and insecure. This component closes this gap.
Used to select an appropriate method to render the free text data. Draws from IANA defined MIME type codes.
Defaults to "text/plain"
This is a telecommunication address (TEL) that is supposed to resolve to precisely the same binary data that could have been sent in the ED.data component directly.
The TEL data type in its TEL.valid_time component allows to announce a deadline time until which the originator of the ED instance promises to keep the reference valid.
Rationale: Large data blocks such as radiographic images can be sent in HL7 messages inline in ED.data. However, there is a need to save network bandwidth by deferring the transmission of such large data blocks until actually needed.
A thumbnail is a low resolution/small image that represents a high-resolution/large image. Thumbnails allow a user to select data more effectively before actually downloading it. The thumbnail concept can be metaphorically used for other data as well, e.g., an movie represented by a shorter clip, an audio by another audio with lower sampling rate, etc.
Rationale: This helps conservation of network bandwidth for large binary data content, such as radiographic images, or catheterization movies.