doc:tools_oodbcreate
no way to compare when less than two revisions
Differences
This shows you the differences between two versions of the page.
— | doc:tools_oodbcreate [2014/03/02 08:08] (current) – created admin | ||
---|---|---|---|
Line 1: | Line 1: | ||
+ | ====== OODB - The own OOBD database format ====== | ||
+ | ===== Why an own database format? ===== | ||
+ | |||
+ | |||
+ | There are some reasons/ | ||
+ | * the main one: There is no real need to have a full flavored super-duper query engine like "'' | ||
+ | * low memory usage: the whole search is file based, memory is only used temporary for the found data | ||
+ | * generic input streams: The db only needs an input stream as source, which is strictly read only in forward direction. By that e.g. encrypted data files can be used. | ||
+ | * high speed: the whole search is just a balanced binary tree lookup, which makes it fast also on slow devices | ||
+ | |||
+ | |||
+ | |||
+ | ===== How to generate such OODB data files? ===== | ||
+ | |||
+ | |||
+ | Such OODB data files are generated by using an csv (comma separated value) input file, where in fact the values are not separated by commas, but by tabs. | ||
+ | |||
+ | Such an input file, which must fulfill the requirements written below, is been translated with the [[https:// | ||
+ | |||
+ | | ||
+ | |||
+ | |||
+ | The outputfile.oobd then belongs into the same directory as the Lua script, which wants to use the database. | ||
+ | |||
+ | ===== The Input file Format ===== | ||
+ | |||
+ | |||
+ | The file format of the input file must be as follow: | ||
+ | |||
+ | HeaderLine \n \\ | ||
+ | Line 1 \n \\ | ||
+ | ... \\ | ||
+ | Line n \n \\ | ||
+ | |||
+ | |||
+ | where | ||
+ | |||
+ | HeaderLine = \\ | ||
+ | (colum_name 0) \\ | ||
+ | [\t (colum_name 1)] \\ | ||
+ | ... \\ | ||
+ | [\t (colum_name n)] | ||
+ | |||
+ | |||
+ | Line = \\ | ||
+ | Key \t Values | ||
+ | |||
+ | Values = \\ | ||
+ | (Value_of_Colum 0) \\ | ||
+ | [\t (Value_of_Colum 1)] \\ | ||
+ | ... \\ | ||
+ | [\t (Value_of_Colum n)] | ||
+ | |||
+ | |||
+ | The input file must be sorted ascending by its keys | ||
+ | |||
+ | If there are more as one Value per key, the Values must sorted in that sequence as they should appear in the later query. | ||
+ | |||
+ | |||
+ | Lines, which begins with an # are seen as comment lines and will be surpressed | ||
+ | |||
+ | ===== The OODB (Output) file Format ===== | ||
+ | |||
+ | The generated output format will be as follows: | ||
+ | |||
+ | HeaderLine 0x0 \\ | ||
+ | Entry 1 \\ | ||
+ | .. \\ | ||
+ | Entry n \\ | ||
+ | |||
+ | Entry = \\ | ||
+ | Key 0x0 \\ | ||
+ | Offset (for key > Searchstring) \\ | ||
+ | Offset (for key < Searchstring) \\ | ||
+ | Value 1 0x0 \\ | ||
+ | [..Values n 0x0] \\ | ||
+ | 0x0 | ||
+ | |||
+ | Offset = \\ | ||
+ | binary unsigned 32-Bit Big Endian, calculated as skip() value from the fileposition after the second 4-Byte value up to the start of the next key string to be evaluated. To distingluish | ||
+ | between an offset of 0 to the next key string and a 0 as the indicator for the end of the search tree, the skip() offset given in the file is always 1 higher as in reality, so 1 needs to be | ||
+ | subtracted to have the correct jump width (e.g. Offset in file: 9 means real jump width 9 -1 = 8 = skip(8) | ||
+ | |||
+ | |||
+ | |||
+ | How to read this file: | ||
+ | < | ||
+ | 1 - Read Headerline (from the file beginning until the first 0x0). Store this data for later naming of the found columns. | ||
+ | 2 - read key value (0x0- terminated String) and the both next 4 Byte long skip() offsets (= relative file positions) for the greater and smaller key value. If they are 0 (zero), there' | ||
+ | 3 - compare key with search string: | ||
+ | - if equal, read attached values in an array. This array then contains the search result(s). Return this and the header line as positive search result. | ||
+ | - if smaller: | ||
+ | if smaller file position is 0 (zero), then return from search with empty result array. | ||
+ | if smaller file position is not 0, jump per skip( value - 1 ) to the file postion of the next index string and continue again with step 2 | ||
+ | - if bigger: | ||
+ | if bigger file position is 0 (zero), then return from search with empty result array. | ||
+ | if bigger file position is not 0, jump per skip(value - 1 ) to the file postion of the next index string and continue again with step 2 | ||
+ | </ |
doc/tools_oodbcreate.txt · Last modified: 2014/03/02 08:08 by admin