ISR11 Operating Instructions for the SMART Text Processing and Document Retrieval System chapter M. E. Lesk Harvard University Gerard Salton Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. II -15 EXPAND a a is either [OCRerr] DOCS, or AT.T. and specifies whether requests only, documents only, or all input is to be expanded. 3.[OCRerr]. Vector Ebcpansion by Means of Concept Hierarchies In addition to statistical means for expanding document vectors, one may wish to expand vectors by means of a pre-assigned concept hierarchy. Various types of relationships between concepts may be specified and used in expansion procedures. The hierarchy conBists of structured trees of concepts, in which each concept has a clearly defined "parent'1, plus a set of "brotherst', and `150n5t1. To designate looser connections, each te[OCRerr] may be assigned a set of "cross-referencesT1. [OCRerr]xpansion involves the intro- duction into the concept vector of the sons and/or brothers and/or father and/or cross-references of each term in the original vector. The selection of the method of expansion is by mean3 of a weighting scheme, and is discussed in part 3.5. To perform a hierarchical expansion the specification HIER a is given where a is either EXPAND or SHRINK. [OCRerr]XPAND indicates that the final vector is to contain the original vector plus the related concepts from the hierarchy; SHRINK indicates that the initial vecto? is delet[OCRerr]d fr[OCRerr]EL the final vector, and only the expanded concepts are used. For exsmple, if it is desired to generalize a vector, each concept could be replaced by its parent using HIER SHRINK; HIER [OCRerr]PAND would merely augment each concept with its parent. EXPAND a serves the same function as CONCO[OCRerr]; a is either RE[OCRerr], DOCS, or AMa and indicates respectively that req[OCRerr]ests, documents, or all input texts are to be expanded.