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Top-down parsing is a strategy of analyzing unknown data relationships by hypothesizing general parse tree structures and then considering whether the known fundamental structures are compatible with the hypothesis.
Bottom-up parsing is parsing strategy that recognizes the text's lowest-level small details first, before its mid-level structures, and leaves the highest-level overall structure to last. [3] In top-down parsing, on the other hand, one first looks at the highest level of the parse tree and works down the parse tree by using the rewriting rules ...
The opposite of this is top-down parsing, in which the input's overall structure is decided (or guessed at) first, before dealing with mid-level parts, leaving completion of all lowest-level details to last. A top-down parser discovers and processes the hierarchical tree starting from the top, and incrementally works its way first downwards and ...
For example, the binary string "110" in the string automaton setting corresponds to the term "1 (1 (0 (nil)))" in the tree automaton setting; this way, strings can be generalized to trees, or terms. The top-down finite tree automaton accepting the set of all terms corresponding to multiples of 3 in binary string notation is then defined by:
In computer science, a recursive descent parser is a kind of top-down parser built from a set of mutually recursive procedures (or a non-recursive equivalent) where each such procedure implements one of the nonterminals of the grammar. Thus the structure of the resulting program closely mirrors that of the grammar it recognizes. [1] [2]
A simple parse tree. A parse tree is made up of nodes and branches. [4] In the picture the parse tree is the entire structure, starting from S and ending in each of the leaf nodes (John, ball, the, hit). In a parse tree, each node is either a root node, a branch node, or a leaf node. In the above example, S is a root node, NP and VP are branch ...
Top-down parsers build the parts of Parse_Tree_Example.svg in the top-down steps numbered here. Used in Bottom-up Parsing. Source Manually drawn by me with Google Docs Date 2012/04/16 Author DBSand. Permission (Reusing this file) See below.
In computer science, an operator-precedence parser is a bottom-up parser that interprets an operator-precedence grammar.For example, most calculators use operator-precedence parsers to convert from the human-readable infix notation relying on order of operations to a format that is optimized for evaluation such as Reverse Polish notation (RPN).