ALT THE GRANFILADE5f1 The granfilade is one of the three major data structures inside the Xanadu system, and probably the simplest. It is used to implement the grandmap, providing a means of looking up atoms by their I-stream addresses. As its name suggests, the granfilade is an enfilade. 5f3The index space used by the granfilade is I-stream tumbler space. The wid of a granfilade crum is a tumbler specifying the span of I-space beneath the crum (i.e., the distance, in tumbler space, from the first to the last bottom crum descended from it). The widdative function is tumbler addition, therefore a crum’s wid is simply the tumbler sum of its children’s wids. Bottom crums have an implicit wid of 0.0.0.0.1 (i.e., spanning no nodes, no accounts, no orgls, no V-spaces and spanning a single atom). Granfilade disps are tumbler offsets in I-space from the parent crum. 5f4Bottom crums in the granfilade represent atoms. Atoms come in two varieties: characters and orgls. Character bottom crums are sto
ALT THE POOMFILADE5g1 5g2The second major data structure inside the system is the poomfilade. The poomfilade is used to implement orgls. POOM stands for Permutations On Ordering Matrix. The poomfilade represents something functionally similar, though not identical, to a permutation matrix: a sparse binary matrix in tumbler space, one axis of which represents the V-stream and the other the I-stream. A “1” at a given coordinate indicates that the orgl realized by the matrix maps that coordinate’s V-stream axis location to and from its I-stream axis location. A “0” indicates that no such mapping exists. This would be a permutation matrix but for virtual copies, which result in a mapping between a single I-stream location and a number of V-stream locations, allowing a given I-stream “column” of this matrix to have more than one “1” entry. In addition, the previously mentioned porosity of tumbler space results in an infinite number of “rows” and “columns” which are all “0”s.
