To better illustrate the difference between logical and graphical information consider some examples. Page layout, fonts etc. are clearly merely visual considerations and have no place in the cantus. A beam is also a visual concern. It details how the music appears on a page but does not carry any inherent information about the music. It is not part of the logical domain.
Similar items are ties, octave signs and barlines.
When representing time signatures in the cantus, only the purely logical information is represented. Note that this linking can be to the actual content of such a formatted output instance, and in theory the links can be created down to the level of individual notes. The multimedia elements will have their own notations and encoding. The aim of using such an infrastructure is to create the capability to handle any type of information, and to be better prepared to handle present and unknown future uses of that information. The WWW is the perfect environment for disseminating SMDL documents.