This paper compares two quite different approaches to estimating costs: a 'bottom-up' approach, represented by the US Department of Veterans Affairs' (VA) Decision Support System that uses local costs of specific inputs; and a 'top-down' approach, represented by the costing system created by the VA
The Equivalence of Bottom-Up and Top-Down Tree-to-Graph Transducers
โ Scribed by Joost Engelfriet; Heiko Vogler
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 979 KB
- Volume
- 56
- Category
- Article
- ISSN
- 0022-0000
No coin nor oath required. For personal study only.
โฆ Synopsis
We introduce the bottom-up tree-to-graph transducer, which is very similar to the usual (total deterministic) bottom-up tree transducer except that it translates trees into hypergraphs rather than trees, using hypergraph substitution instead of tree substitution. If every output hypergraph of the transducer is a jungle, i.e., a hypergraph that can be unfolded into a tree, then the tree-to-graph transducer is said to be tree-generating and naturally defines a tree-to-tree translation. We prove that bottom-up tree-to-graph transducers define the same treeto-tree translations as the previously introduced top-down tree-to-graph transducers. This is in contrast with the well-known incomparability of the usual bottom-up and top-down tree transducers.
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