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Deleting Known Field Values

In CM-Well, it's legal for a single field to have more than one value.

Here is an example where someField has 2 values:

<http://example.org/my/infoton> <http://ont.example.org/v1.0/ns#someField> "value#1" .
    <http://example.org/my/infoton> <http://ont.example.org/v1.0/ns#someField> "value#2" .

Suppose we want to preserve value#1 and delete value#2.

One way to do it is with the markReplace operator:

<http://example.org/my/infoton> <cmwell://meta/sys#markReplace> <http://ont.example.org/v1.0/ns#someField> .
    <http://example.org/my/infoton> <http://ont.example.org/v1.0/ns#someField> "value#1" .

This command deletes all the values in someField and writes value#1 to someField. (We could also use the replace-mode flag, which implicitly adds a markReplace statement to every ingested field.) But this method may cause unexpected results.

The other way is to use the markDelete operator to specifically delete the unwanted value:

<http://example.org/my/infoton> <cmwell://meta/sys#markDelete> _:anon .
    _:anon <http://ont.example.org/v1.0/ns#someField> "value#2" .

The reason to use markDelete, when you know what value you want to delete, is that you know exactly which values will be deleted. The markReplace command deletes all existing fields before writing the new value. Therefore, using this command might delete some values added by another user, which was not the intention of the user calling markReplace.

Therefore, to delete one or more specific field values, we recommend using the markDelete operator.