We propose to reformulate metadata templates such that they represent changes that occur within the RTS.

Each metadata template represents a change in the RTS, where a change is typically something that happens to a template. We currently recognize three major changes that happen in an RTS: insertion of a template into the RTS (essentially creation), invalidation of an existing template, and re-validation of a template (that was previously invalidated). We describe these changes below. Also, assignment of an instance unique identifier (IUI) is something that happens in the RTS. Currently, these changes are captured in A templates. At this time, we do not propose to change how IUI assignments are captured as A templates.

The original formulation of metadata templates has a parameter, the "error or insertion" code (E), whose semantics are mixed. If you are inserting a template for whatever reason, the E code is set to the value I for "insertion". If you are correcting an error, then the E parameter codifies what type of error exists in the RTS that makes the template false (even if the error originates with another template. For example, a duplicate IUI assignment in an A template causes a PtoU template to be incorrect, but in inserting a metadata template to correct the PtoU template, you assign the E parameter the value U5).

Note that we never change or update any parameter in a template or metadata template in an RTS. To correct errors, we insert new metadata templates. This practice enables us to view the state of the RTS as it was at any time in the past.

The Proposal

We propose to remove the E parameter from metadata template specification, and replace it with two parameters: the CT parameter for change type and the EC parameter for error code.

The CT parameter

The CT parameter may take 3 values, defined as follows. It is a required field in the metadata template.

Parameter value	Definition
I	The template referred to by this metadata template was inserted into the RTS by the entity designated by iui_d
X	The template referred to by this metadata template was invalidated by the entity designated by iui_d
R	The template referred to by this metadata template was re-validated by the entity designated by iui_d

A template may be invalidated then revalidated and subsequently invalidated again and etc. any number of times through the history of the RTS. There will be a new metadata template for each insertion, invalidation, and revalidation.

The original metadata template specification did not envision the possibility that assertions that templates are in error might themselves be made in error. And thus there was no mechanism to restore templates mistakenly asserted to be in error. Thus the "change view" has improved the flexibility of RT.

One disadvantage to this approach is that to query "good" data in the RTS, the query must check disjunctively for the values I and R in the CT parameter. Alternatively, we could add a flag to the templates themselves that determines whether they are valid. This flag would be set to true upon insertion and revalidation, and to false upon invalidation. The disadvantage to that approach is keeping the flag in synchronization with the information in the metadata templates in the RTS.

The EC parameter

The EC parameter takes the same values as the original E parameter except for the value I (insertion). It is not a required field in the case of template insertion or revalidation. It would be required for any metadata template with an CT parameter with value X.

The C parameter

The C (change reason) parameter continues to exist as before. However, we replace error correction (XM) with error recognition (XR) as an allowed value.

Consider an incorrect PtoU template asserting that a particular chair is an instance of Table. The error was in asserting this PtoU template, not in inserting it into the RTS. Thus, the error was made on the part of the entity designated by iui_a (in the PtoU template). Now either this entity (1) really believed that the chair was a table for some reason or (2) made a mistake in picking out a reference to the type Chair (e.g., said "table" when she meant to say "chair" or selected "table" from the dropdown list when she meant to select "chair").

Now, if the entity correcting the error is the same entity as the iui_a of the template with the error, then there is the possibility of both change in belief (really believed it was a table when she made the PtoU assertion) and recognition of error (never believed it was a table but just picked the wrong reference somehow).

If the entity correcting the error is a different entity, the same two possibilities exist: the entity may have shared the incorrect belief or it may just have recognized the error (and not have believed it was a table).

We cannot assume either. The remaining question is whether it is worth making the distinction? It would certainly be helpful in the grand scheme of things to capture both, so we could differentiate erroneous beliefs from errors in recording those beliefs, so that we could study them.

The allowed values for C are therefore the following:

Parameter	Definition
CE	The change in the RTS occurred to reflect a change in reality.
CB	The change in the RTS occurred to reflect a change in belief.
CR	The change in the RTS occurred to reflect a change in relevance.
XR	The change in the RTS occurred to reflect a recognition of error. It is different from a change in belief, because the entity making the change never believed what the RTS said, but instead recognized that the statement in the RTS was wrong. It could be, for example, that s/he meant to select the universal Liver from a pick list, but accidentally picked Lung and only later after recording data in the RTS realized the mistake.

Implications for Remainder of Metadata Template

Parameter	Implication
iui_d	Now refers to the entity that is initiating the change/event in the RTS.
t_d	Now refers to the time at which the change occurs.
iui_t	Still refers to the A, PtoU, PtoP, etc. template, but now the implication is that this template has participated in a change to the RTS (e.g., its insertion is a change to the RTS)
S	Now refers to a list of templates that correct the error in the template denoted by iui_t (formerly referred to templates that "replaced" template denoted by iui_t but we do not recognize replacement of templates, just invalidation and revalidation).

Possible Combinations of Parameter Values

CT	C	EC	S
I	<any>	<null>	<null>
X	XR or CB	<any>	<any>
R	XR or CB	<null>	<null>

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