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hierarchical_model

hierarchical_model - HIERARCHICAL MODEL(DL/I MODEL Field...

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HIERARCHICAL MODEL (DL/I MODEL) Field Segment Database record (type) Database ONLY ONE TOO MANY RELATIONSHIPS ARE ALLOWED FACULTY STUDENT STU STU CLASS CL-PTR STU-PTR FAC STU DEPT ST-PTR CLASS DEPT FAC CLASS STU STU FAC ST-PTR ST-PTR CLASS CL-PTR
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The hierarchical data model has the following characteristics : 1. There is a set of segments (record types) { R 1 , R 2 ,…, R n }. 2. There is a set of relationships connecting all segments in one data structure diagram. 3. There is no more than one relationship between any two segments R i and R j . Hence relationships need not be labeled. 4. The relationships expressed in the data structure diagram form a tree with all arcs pointing towards leaves. 5. Each relationship is 1:N, and it is total – that is for every R j segment occurrence, there is exactly one R i segment occurrence connected to it, if R i is the parent of R j in the definition tree. Storage structures for hierarchical database : 1. Any way you store a tree 2. Linked List 3. Sequential file (tree scanned via LNR, NLR, etc.)
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