A Blockchain-Based Location Privacy-Preserving Scheme in Location-Based Service

Algorithm 2

Construct personal semantic tree.

Input:

 DSetloc (The Personal Request Location Set), ε (The threshol);

Output:

 The Personal semantic tree, T;

1: Initializes the hierarchical trees T={E,V} and V.layer [0]=Root;

2: Extract the semantic features of the location, including TSF,GSF;

3: Initializes Group={Groupi} (i=1,2,…n) based on its GSF similarity, j=1;

4: for Each i in Len (DSetloc) do

5: if loci.GSF == loci+1.GSF then

6:  Group [j].add (loci);

7:  j + +;

8: end if

9: end for

10: V.layer [1].append (Group.GSF);

11:

12: for Each group in Group do

13: centerm=clusterEM (N, locj.TSF, ε),locj.TSF ∈group; //EMcluster cluster method

14: Caculating the distance Dis (centerm, locj.TSF) between center i and locj;

15: Choose locj which meet Dis (centerm, locj.TSF)<ε to put into Cm;

16: Put Cm into C;

17: end for

18: V.layer [2].append (C);

19: Put locs into corresponding cluster Cm as its V.leafnode;

20: Put V into T;

21: return T;