Index Representation of Trees
A tree structure can readily be represented using indexes. The technique is to store each one-to-many
relationship as an index. These lists are then used to match parents and children.
Using the VENDOR and INVOICE records in Figure H-19, we see that VENDOR AA (in RRN1) owns IN-
VOICEs 110 (RRN7) and 118 (RRN3). Thus, RRN1 is the parent of RRN7 and RRN3. We can represent this
fact with the index in Figure H-24. The list simply associates a parent’s address with the addresses of
each of its children.
If the tree has several 1:N relationships, several indexes will be required—one for each relationship. For
example, for the structure in Figure H-13, five indexes are needed.
How Can We Represent Simple Networks?
As with trees, simple networks can also be represented using linked lists and indexes.
Linked-List Representation of Simple Networks
Consider the simple network shown in Figure H-25. It is a simple network because all of the relationships
are 1:N, and the SHIPMENT records have two parents of different types. Each SHIPMENT has a CUS-
TOMER parent and a TRUCK parent. The relationship between CUSTOMER and SHIPMENT is 1:N because
a customer can have several shipments, and the relationship from TRUCK to SHIPMENT is 1:N because
Index Representation of TreesA tree structure can readily be represented using indexes. The technique is to store each one-to-manyrelationship as an index. These lists are then used to match parents and children.Using the VENDOR and INVOICE records in Figure H-19, we see that VENDOR AA (in RRN1) owns IN-VOICEs 110 (RRN7) and 118 (RRN3). Thus, RRN1 is the parent of RRN7 and RRN3. We can represent thisfact with the index in Figure H-24. The list simply associates a parent’s address with the addresses ofeach of its children.If the tree has several 1:N relationships, several indexes will be required—one for each relationship. Forexample, for the structure in Figure H-13, five indexes are needed.How Can We Represent Simple Networks?As with trees, simple networks can also be represented using linked lists and indexes.Linked-List Representation of Simple NetworksConsider the simple network shown in Figure H-25. It is a simple network because all of the relationshipsare 1:N, and the SHIPMENT records have two parents of different types. Each SHIPMENT has a CUS-TOMER parent and a TRUCK parent. The relationship between CUSTOMER and SHIPMENT is 1:N becausea customer can have several shipments, and the relationship from TRUCK to SHIPMENT is 1:N because
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