Nonreplicated Static Data Allocation in Distributed Databases Using Biogeography-Based Optimization

Table 1

Description of various notations.

Symbol	Meaning
𝑆	The set of all sites
𝑛	The number of sites in the network
𝑆𝑖	The ith site
𝑄	The set of all queries
𝑞	The number of distributed database queries
𝑄𝑗	The jth query
𝐹	The set of all fragments
𝑚	The number of data fragments in the database system
𝐹𝑘	The kth fragment
FR𝑖𝑗	The execution frequency of the jth query at ith site
RF𝑗𝑘	The retrieval frequency to the kth fragment by jth query
𝑅𝑗𝑘	Percentage of kth fragment needed for retrieval by jth query
UF𝑗𝑘	The update frequency to the kth fragment by jth query
𝑈𝑗𝑘	Percentage of kth fragment needed to be updated by jth query
CC𝑖,𝑖′	The communication cost from site 𝑆𝑖 to site 𝑆𝑖′
Size (𝐹𝑘)	Size of the kth fragment
RC	Retrieval cost
UC	Update cost
TC	The total data transfer cost