Databases, mental situations and the effects of mental events

For the moment it isn't isn't clear whether we shall want
to distinguish between databases and mental situations.  However,
the actions and other events we want to provide for include more
than is traditional with databases.

A database includes a collection of sentences.  There may be
even more structure, e.g. the pedigrees of sentences that are
used in TMSs.  However, we can imagine this additional information
to itself be represented by sentences.  These sentences may be
real or virtual, i.e. the information may be represented in some other way
than by actual sentences, but it can be considered to have logical
consequences just as though it were represented by sentences.

Even considered as a set of sentences the database contains more
information than the theory consisting of its consequences (or
the set of its models).  For example, the databases {p,q}
and {p,p iff q} have the same logical consequences but different
behavior under the event (delete p).

Let's define  theory(db)  to be the set of all logical consequences
of the sentences of the database  db.  exttheory(db)  is the
set of all consequences about the external world of the sentences of
the database  db.  Since if  db  contains information about the
pedigrees of sentences,  theory(db)  may contain a lot of
internal information,  exttheory  may be useful.  The equivalence
relation

exttheory(db1) = exttheory(db2)

is probably of interest.

In some mental event systems mental events will be logged in
the database, e.g. the occurrence of  (delete p)  will cause
p  to be deleted but might also enter   (deleted p <time>)  into
the database.

Now we need a small catalog of interesting types of mental events
as well as more components of the mental state.

1. Establishing a goal makes other goals plausible.
2. a goal is on the stack