There are some attributes of a PI Tag that simply
cannot be changed. Those are system created.
Things like the record of who created the tag, when it was
created, when, when it was changed, who
changed it, that type of thing. So those are things that,
you know, more or less you are stuck with those
because they are system generated.
Here is an example of those. We go over to our
Point Builder in System Management Tools.
I have selected a tag. If you go into System, this is going to show
you those System Attributes. These are things
that we really cannot change.
Now for some reason you need to rename a tag, you can do that.
That, that's not a problem. It will preserve all the history
and it will not have any effect on things like ProcessBook
and DataLink or, excuse me on Pro... on PI ProcessBook,
because ProcessBook makes reference to these tags with
their Internal ID. Now, maybe you did not see this
a little earlier but, if you look at this, this is the PointID.
Each tag has a PointID. This is the tag
Sinusoid, and it's the first tag that's
created in every PI System. As I said, it's one of those default PI
Tags. If you do create the default tags, then
this is going to be your Point #1. And that's, in fact,
how we store the reference to that tag
within ProcessBook. However, DataLink is an add-in
to Excel, and we simply hard-code the name
of the tag in DataLink. So any type of DataLink
Reports -- after you edit the name of a tag, you are
going to have to change those DataLink Reports. Also, if you have got
any performance equations or performance equation
expressions that are making use
of PI Tags -- in other words, there is a
PI Tag name embedded in a performance equation expression --
then that's going to continue to work up until the point
when -- at which you, you stop
and restart Performance Equations. And so that's,
that's something -- obviously you need to edit that. So,
better to edit after making changes --
anything that may be affected by that. Unfortunately,
we do not really have any kind of a,
any kind of a notification to let you know which tags
are going to be affected by an edit to a name chan... --
or to a tag name. So, that's something you are going to have to look for
using tag searches and looking for the, the
different attributes of your, your different Performance
Equation Tags or tags that use Performance Equation Syntax.
Now, same for deleting a tag.
Deleting a tag is going to have some
ramifications. First of all, it's
going to delete all the archive data that's
associated with that tag. Actually,
we should be careful the way we say that. We do not
delete the archived data. We just make it so that you
cannot get to it anymore, which is more or less the same thing.
So, although it is possible to recover that
situation, be very careful about deleting a tag. It's
kind of a, a nightmarish set of
procedures that you will have to step through with Tech Support
to recover the data from a deleted PI Tag.
And, and as you will see, there is no
quick undelete to that, so -- because
it is such a severe problem if you delete the wrong one.
Now one of the things we suggest you do is just turn the
Scan Attribute to Off and see if anybody complains that you are not looking at
that data anymore, or you are not able to see that current data.
That will still allow people to look at historical data.
So, also, we suggest you keep a copy of the
configuration of all your tags since
things like the PointID, the Record Number, those things are going to
be required if you do try to do a recovery. What we have
seen some sites do is, they kind of collect up,
store up tags for deletion, and then only delete them once per
quarter or so. So, they set things to Scan
Off, just make sure nobody is actively using that
data, and then they are, when they are good and ready and they have proved to themselves
they are not going to be shooting themselves in the foot, then they will go ahead
delete the tags.