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diff --git a/docs/html/xbc8.html b/docs/html/xbc8.html deleted file mode 100755 index fcc461c..0000000 --- a/docs/html/xbc8.html +++ /dev/null @@ -1,79 +0,0 @@ -<!DOCTYPE HTML PUBLIC> -<HTML> -<TITLE>Xbase DBMS Chapter 8</TITLE> -<BODY BGCOLOR=#FFFFFF> -<H2><p align="center">MDX Indices</p></H2> -<p align="center">Chapter Updated 12/02/22</p><hr> - -The objective of this chapter is to provide information regarding the -basic concepts of how .MDX index files work in the Xbase environment.<br><br> - -The information in this chapter has been gathered by searching the internet -and by examining the structure of known good <DX indexes.<br><br> - -<h4>MDX Index File Characteristics</h4> - -<li>MDX files are the same name as the corresponding DBF file with an MDX extension. -<li>MDX files are automatically opened by the library when the DBF file is opened. -<li>MDX index files (aka prod indices) contain from one to 47 tags, where each tag has it's own key characteristics. -<li>MDX indices maintain keys in either ascending or descending sort order. -<li>MDX indices support filtered keys. For example, a filter of <b>.NOT. DELETED()</b> will keep deleted records out -of the index tag. -<li>MDX indices are automatically updated by the Xbase library after the -indices are opened. - -<li>MDX indices support <em>unique</em> or <em>non unique</em> keys.<br><br> - -<em>Unique</em> keys must be unique if the UniqueKeyOption is not set to XB_EMULATE_DBASE. -If the UniqueKeyOption is set to XB_EMULATE_DBASE, then the database update routines will -add a record to the table, but not add a corresponding duplicate key to the index tag. -The UniqueKeyOption is off (don't allow duplicates) by default. -<br><br> - -<em>Non-unique</em> Keys are not required to be unique, duplicate -keys are allowed if the index is created with the XB_NOT_UNIQUE -setting. Duplicate keys are stored in record number order.<br><br> - - -<li>Character keys are left justified and padded on the right with spaces. -<li>Numeric keys are stored as twelve byte BCD values. -<li>Date keys are stored as eight byte double julian values. - -<h4>MDX File Internals</h4> - -The following information is not needed to use the library, it is just included -for general information.<br><br> - -MDX files are comprised of 512 pages where multiple pages make a block. The default -setting is 1024 blocks, each block containing two pages.<br><br> - -The first four pages contain: -<li>Bytes 0 - 543 contain general file information. -<li>Bytes 544 - 2047 is a 47 item table containing specific tag information. -<br><br> - -Pages five and beyound: -<li>Bytes 2048 and beyond contain tag header blocks, interior nodes and leaf nodes. - -<br><br> - -<h4>Interior and Leaf Nodes</h4> - -Interior Nodes and Leaf Nodes share the same structure in an NDX file with -the exception that interior nodes have a non zero number immediately -after the rightmost key on the node. - -Interior nodes point to other interior nodes or leaf nodes and leaf nodes point -to records in a DBF file. Interior nodes are optional nodes in an MDX file, -however if there are more than a few keys in the index there will -certainly be one or more interior nodes in the file. There will -always be at least one leaf node per tag in the file. Leaf nodes -contain DBF record numbers which point to the location of the record -in the DBF file.<br><br> - -<br><br> - -<hr> -<p><img src="xbase.jpg"><br><hr> -</BODY> -</HTML> |