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--- doc:oodbcreate [2012/07/26 08:15] – admin
+++ doc:oodbcreate [2014/03/02 08:08] (current) – removed admin
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-====== OODB - The own OOBD database format ======
-===== Why an own database format? =====
-There are some reasons/advantages to set up an own format for the OOBD database:
-  * the main one: There is no real need to have a full flavored super-duper query engine like "''SELECT this, that FROM here, there WHERE all=nothing..''", a simple key -> value(s) lookup is all we mostly need
-  * 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://code.google.com/p/oobd/source/browse/trunk/tools/oodbcreate/|oodbCreateCli]] php script:
-   oodbCreateCli inputfile.csv > outputfile.oobd
-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] \\
-x0
-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:
-<code>
-- Read Headerline (from the file beginning until the first 0x0). Store this data for later naming of the found columns.
-- 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's no more smaller or greater key available
-- 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
-</code>