| This directory contains an SQLite extension that implements a virtual | |
| table type that allows users to create, query and manipulate r-tree[1] | |
| data structures inside of SQLite databases. Users create, populate | |
| and query r-tree structures using ordinary SQL statements. | |
| 1. SQL Interface | |
| 1.1 Table Creation | |
| 1.2 Data Manipulation | |
| 1.3 Data Querying | |
| 1.4 Introspection and Analysis | |
| 2. Compilation and Deployment | |
| 3. References | |
| 1. SQL INTERFACE | |
| 1.1 Table Creation. | |
| All r-tree virtual tables have an odd number of columns between | |
| 3 and 11. Unlike regular SQLite tables, r-tree tables are strongly | |
| typed. | |
| The leftmost column is always the pimary key and contains 64-bit | |
| integer values. Each subsequent column contains a 32-bit real | |
| value. For each pair of real values, the first (leftmost) must be | |
| less than or equal to the second. R-tree tables may be | |
| constructed using the following syntax: | |
| CREATE VIRTUAL TABLE <name> USING rtree(<column-names>) | |
| For example: | |
| CREATE VIRTUAL TABLE boxes USING rtree(boxno, xmin, xmax, ymin, ymax); | |
| INSERT INTO boxes VALUES(1, 1.0, 3.0, 2.0, 4.0); | |
| Constructing a virtual r-tree table <name> creates the following three | |
| real tables in the database to store the data structure: | |
| <name>_node | |
| <name>_rowid | |
| <name>_parent | |
| Dropping or modifying the contents of these tables directly will | |
| corrupt the r-tree structure. To delete an r-tree from a database, | |
| use a regular DROP TABLE statement: | |
| DROP TABLE <name>; | |
| Dropping the main r-tree table automatically drops the automatically | |
| created tables. | |
| 1.2 Data Manipulation (INSERT, UPDATE, DELETE). | |
| The usual INSERT, UPDATE or DELETE syntax is used to manipulate data | |
| stored in an r-tree table. Please note the following: | |
| * Inserting a NULL value into the primary key column has the | |
| same effect as inserting a NULL into an INTEGER PRIMARY KEY | |
| column of a regular table. The system automatically assigns | |
| an unused integer key value to the new record. Usually, this | |
| is one greater than the largest primary key value currently | |
| present in the table. | |
| * Attempting to insert a duplicate primary key value fails with | |
| an SQLITE_CONSTRAINT error. | |
| * Attempting to insert or modify a record such that the value | |
| stored in the (N*2)th column is greater than that stored in | |
| the (N*2+1)th column fails with an SQLITE_CONSTRAINT error. | |
| * When a record is inserted, values are always converted to | |
| the required type (64-bit integer or 32-bit real) as if they | |
| were part of an SQL CAST expression. Non-numeric strings are | |
| converted to zero. | |
| 1.3 Queries. | |
| R-tree tables may be queried using all of the same SQL syntax supported | |
| by regular tables. However, some query patterns are more efficient | |
| than others. | |
| R-trees support fast lookup by primary key value (O(logN), like | |
| regular tables). | |
| Any combination of equality and range (<, <=, >, >=) constraints | |
| on spatial data columns may be used to optimize other queries. This | |
| is the key advantage to using r-tree tables instead of creating | |
| indices on regular tables. | |
| 1.4 Introspection and Analysis. | |
| TODO: Describe rtreenode() and rtreedepth() functions. | |
| 2. COMPILATION AND USAGE | |
| The easiest way to compile and use the RTREE extension is to build | |
| and use it as a dynamically loadable SQLite extension. To do this | |
| using gcc on *nix: | |
| gcc -shared rtree.c -o libSqliteRtree.so | |
| You may need to add "-I" flags so that gcc can find sqlite3ext.h | |
| and sqlite3.h. The resulting shared lib, libSqliteRtree.so, may be | |
| loaded into sqlite in the same way as any other dynamicly loadable | |
| extension. | |
| 3. REFERENCES | |
| [1] Atonin Guttman, "R-trees - A Dynamic Index Structure For Spatial | |
| Searching", University of California Berkeley, 1984. | |
| [2] Norbert Beckmann, Hans-Peter Kriegel, Ralf Schneider, Bernhard Seeger, | |
| "The R*-tree: An Efficient and Robust Access Method for Points and | |
| Rectangles", Universitaet Bremen, 1990. | |