51
sentable as a composition of operations like move and copy or transpose and copy.
2
In-
formally, permutational operations affect only the address spaceof a composite.
• Content-dependentoperations are ones whose function depends on the actual values
stored in a composite. Like purely permutational operations, they may depend on struc-
tural properties of a composite, but they are different in kind, because of their effect
depends on the actual items stored in the sequence. Examples are operations like sort
paragraphs, transform character-encoding, orsubstitute string.They may only affect a
small region of a sequence, but they fundamentally depend on the exact data stored in
that sequence. The scope of these operations may also vary from a localscope, as in the
sorting a set or paragraphs, to a globalscope encompassing the entire composite. This
kind of global operation might record a global change or a sorting constraint that should
be applied to a shared object in a persistent way. Editing interfaces that support such
operations have become widely available in graphical editors like Photoshop, which can
save edits and intermediate states of a picture and reapply them at a later time. Photo-
shop retains a static record of all changes applied by the artist and then allows them to
be reapplied dynamically on request.
2
For a sequence, move and transpose are formally identical operations. Their effects are the same,
but move distinguishes one of the two transposed sections as the “one being moved”. This has impli-
cations for merge, as it provides additional information about the user’s intent in making an edit.
Composed transpositions are capable of generating all the permutations of a sequence. We have not
discussed the possibility of movement betweensequences, but this is an example of a useful and
straightforward extension of the semantics of move, and one that is not even sensible for a transpose
operation. This kind of support is especially important when composed sequences are used to repre-
sent hierarchical document structures.
sentable as a composition of operations like move and copy or transpose and copy.
2
In-
formally, permutational operations affect only the address spaceof a composite.
• Content-dependentoperations are ones whose function depends on the actual values
stored in a composite. Like purely permutational operations, they may depend on struc-
tural properties of a composite, but they are different in kind, because of their effect
depends on the actual items stored in the sequence. Examples are operations like sort
paragraphs, transform character-encoding, orsubstitute string.They may only affect a
small region of a sequence, but they fundamentally depend on the exact data stored in
that sequence. The scope of these operations may also vary from a localscope, as in the
sorting a set or paragraphs, to a globalscope encompassing the entire composite. This
kind of global operation might record a global change or a sorting constraint that should
be applied to a shared object in a persistent way. Editing interfaces that support such
operations have become widely available in graphical editors like Photoshop, which can
save edits and intermediate states of a picture and reapply them at a later time. Photo-
shop retains a static record of all changes applied by the artist and then allows them to
be reapplied dynamically on request.
2
For a sequence, move and transpose are formally identical operations. Their effects are the same,
but move distinguishes one of the two transposed sections as the “one being moved”. This has impli-
cations for merge, as it provides additional information about the user’s intent in making an edit.
Composed transpositions are capable of generating all the permutations of a sequence. We have not
discussed the possibility of movement betweensequences, but this is an example of a useful and
straightforward extension of the semantics of move, and one that is not even sensible for a transpose
operation. This kind of support is especially important when composed sequences are used to repre-
sent hierarchical document structures.
