Method of generating search trees and navigation device

1. A method of generating search trees indicating next valid characters for an input interface of a navigation device, said method comprising:

retrieving information on a first set of character strings and information on a second set of character strings, said first and second sets being different from each other;

determining, based on said information on said first set and said information on said second set, a search sub-tree which indicates next valid characters for both a subset of said first set of character strings and another subset of said second set of character strings;

generating a first search tree based on said information on said first set and a second search tree based on said information on said second set, wherein said first search tree and said second search tree are generated such that a node of said first search tree references said search sub-tree and that another node of said second search tree references said search sub-tree, wherein the first search tree and second search tree comprise different search trees having no common nodes; and

storing said search sub-tree, first search tree and said second search tree in a data base, wherein only one instance of the search sub-tree is stored in the data base for the first search tree and the second search tree.

2. The method of claim 1 , wherein said determining comprises:

generating a first provisional search tree based on said information on said first set, wherein said first provisional search tree has a leaf node for each character string included in said first set;

generating a second provisional search tree based on said information on said second set, wherein said second provisional search tree has a leaf node for each character string included in said second set;

comparing said first provisional search tree and said second provisional search tree to determine said search sub-tree.

3. The method of claim 2 , wherein said determining comprises:

identifying a portion of said first provisional search tree which is identical to a portion of said second provisional search tree.

4. The method of claim 3 , wherein said generating said first search tree comprises:

truncating said first provisional search tree based on said identified portion; and

adding a reference to said search sub-tree at a node of said truncated first provisional search tree.

5. The method of claim 4 ,

wherein said second search tree includes said search sub-tree,

wherein said node of said first search tree references a node of said second search tree which is included in said search sub-tree.

6. The method of claim 3 , wherein said generating said second search tree comprises:

truncating said second provisional search tree based on said identified portion; and

adding a reference to said search sub-tree at a node of said truncated second provisional search tree.

7. The method of claim 6 , wherein said first search tree, said second search tree and said search sub-tree are stored as separate binary large objects.

8. The method of claim 1 , wherein said first set of character strings and said second set of character strings are selected from country names, city names, street names, or names of points of interest (POI).

9. The method of claim 1 , further comprising:

retrieving information on at least one further set of character strings different from said first set and said second set;

wherein said search sub-tree is determined based on said information on said first set, said information on said second set and said information on said at least one further set, such that said search sub-tree indicates next valid characters for a subset of said first set, a subset of said second set, and a subset of said at least one further set; and

generating at least one further search tree based on said information on said at least one further set, such that a node of said at least one further search tree references said search sub-tree.

10. A navigation device, comprising:

an input interface configured to receive character input in a sequential manner;

a data base storing plural search trees which respectively indicate next valid characters for a name input received at said input interface, wherein a first search tree has a first node referencing a search sub-tree and a second search tree has a second node referencing the same search sub-tree, wherein the first search tree and second search tree comprise different search trees having no common nodes, wherein only one instance of the search sub-tree is stored in the data base for the first search tree and the second search tree; and

a processing device coupled to said input interface and said data base to perform a next valid character search, said processing device being configured

to determine, when a character input is received at said input interface, next valid characters using at least one of said plural search trees stored in said data base; and

to selectively continue said next valid character search in said search sub-tree when reaching either one of said first node of said first search tree or said second node of said second search tree.

11. The navigation device of claim 10 , wherein the data base stores plural search sub-trees, each of which is respectively referenced by nodes of at least two different search trees.

12. The navigation device of claim 10 , wherein said processing device is configured to pre-load said search sub-tree prior to reaching said first node or said second node in said next valid character search.

13. The navigation device of, claim 10 , wherein said search sub-tree is included in one of said first search tree and said second search tree.

14. The navigation device of claim 10 , wherein said search sub-tree is stored in said data base separately from said first search tree and said second search tree.

15. The navigation device of claim 10 , wherein each one of said first and second search trees indicates next valid characters for country names, city names, street names, or names of points of interest (POI).