Types of Digital Objects - Advanced Digital Preservation - page 38

4.3 Static vs. Dynamic
Digital objects do (usually) need software and hardware to extract information from
the bits - as discussed in Sect. 1.1 . Static objects are ones which, unless they are
transformed, are unchanged as bit sequences. These we will refer to as Static Digital
Objects .
On the other hand we can think about database files which naturally change over
time as entries are changed. Alternatively we can consider a whole collection of files
as the data object. Such a collection might change as additional files are added to
the collection over time. Such digital objects we will refer to as Dynamic Digital
Objects .
Of course at any particular time the Dynamic Digital Object is a particular Static
Digital Object which we may preserve. On the other hand it may be of interest, in
the case of a Dynamic Digital Object, to know what the state of the object was at
any particular time. In fact some would argue that most datasets change over time
and the state at each particular moment in time may be important. This is an impor-
tant area requiring further research; however from the point of view in this topic
it may be useful to break the issue into separate parts. At each moment in time
we could, in principle, take a snapshot and store it. That snapshot has its associ-
ated Representation Network. Efficient storage of a series of snapshots may lead
one to store differences or include time tags in the data. Additional Representation
Information would be needed which describes how to get to a particular time's
snapshot from the efficiently encoded version.
4.4 Active vs. Passive
One other useful distinction is between what may be called active and passive digital
objects.
By Passive Digital Object we mean something with which things are done, for
example used by other applications (software) to do something. For example a doc-
ument file is used by a word processing programme to print the document or display
it on the screen, or an astronomical image in a FITS file would be used by astro-
nomical analysis software to do scientific research. Such digital objects are often
referred to as “data” but since the term Data Object is already used by OAIS we
prefer the term Passive Digital Object.
An Active Digital Object on the other hand does something. For example the
word processing application or the astronomical analysis software mentioned in the
previous paragraph might be the digital objects to be preserved.
Once again there will always be fuzzy boundaries, so one could consider an
Access[TM] database as a Passive Digital Object - used by the Access software -
but it could easily itself contain software (for example some form of BASIC) which
would mean that it could be considered to be an Active Digital Object.