doc:oodbcreate
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- | ====== OODB - The own OOBD database format ====== | ||
- | Why an own database format? | ||
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- | 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 for the found data | ||
- | * generic inputstreams: | ||
- | * high speed: the whole search is just a balanced binary tree lookup, which makes it fast also on slow devices | ||
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- | How to generate such OODB data files? | ||
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- | 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. | ||
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- | Such an input file, which must fulfill the requirements written below, is been translated with the [[https:// | ||
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- | | ||
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- | The outputfile.oobd then belongs into the same directory as the Lua script, which wants to use the database. | ||
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- | ===== Input file Format ===== | ||
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- | The file format of the input file must be as follow: | ||
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- | HeaderLine \n | ||
- | Line 1 \n | ||
- | .. | ||
- | Line n \n | ||
- | |||
- | 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) | ||
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- | The input file must be sorted ascending by its keys | ||
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- | If there are more as one Value per key, the Values must sorted in the sequence as they should be used later | ||
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- | ===== Input file Format ===== | ||
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- | The generated output format will be as follows: | ||
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- | HeaderLine 0x0 | ||
- | Entry 1 | ||
- | .. | ||
- | Entry n | ||
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- | Entry = Key 0x0 (Offset, if key > Searchstring) (Offset, if key < Searchstring) Values 1 0x0 [..Values n 0x0] 0x0 | ||
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- | 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 | ||
- | substracted to have the correct jump width (e.g. Offset in file: 9 means real jump width 9 -1 = 8 = skip(8) | ||
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- | How to read this file: | ||
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- | 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 (string until the next 0x0) and the both next 4 Byte long skip() offsets (= relativefile 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() 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() to the file postion of the next index string and continue again with step 2 | ||
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- | */ |
doc/oodbcreate.1343238083.txt.gz · Last modified: 2012/07/25 19:41 by admin