Weka/experiment/DatabaseUtils.props

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Table of contents

1 Description 2 Version 3 Fields 4 Database type mapping 5 See also

Description

Defines the database setup, i.e., JDBC driver information, JDBC URL, database type conversion, etc.

Version

• >= 3.1.3

Fields

• General
  • jdbcDriver
    the comma-separated list of jdbc drivers to try loading
  • jdbcURL
    the JDBC URL to the database
• Table creation
  • CREATE_STRING
    database specific datatype, e.g., TEXT
  • CREATE_INT
    database specific datatype, e.g., INT
  • CREATE_DOUBLE
    database specific datatype, e.g., DOUBLE
• Database flags
  • checkUpperCaseNames
    necessary if database turns column names into upper case ones, e.g., HSQLDB
  • checkLowerCaseNames (> 3.5.3)
    necessary if database turns column names into lower case ones, e.g., PostgreSQL
  • checkForTable (> 3.5.3)
    Checks whether the tables in the query are available in the meta-data of the JDBC Connection. Some tables, like pg_tables, exist but are not available through the meta-data
  • setAutoCommit
    setting for java.sql.Connection.setAutoCommit(boolean)
  • createIndex
    whether to create a primary key Key_IDX in the results table of an experiment
• Special flags for DatabaseLoader/Saver (package weka.core.converters)
  • nominalToStringLimit (>= 3.4.1)
    beyond this limit, nominal columns are loaded as STRING attributes and no longer as NOMINAL ones
  • idColumn (>= 3.4.1)
    unique key in table that allows ordering for incremental loading

Database type mapping

In order to import the data from database correctly into Weka, one has to specify what JDBC datatype corresponds to what Java SQL retrieval method. Here's an overview of how the Java types are mapped to Weka's attribute types:

Java type	Java method	Identifier	Weka attribute type	Version
String	getString()	0	nominal
boolean	getBoolean()	1	nominal
double	getDouble()	2	numeric
byte	getByte()	3	numeric
short	getByte()	4	numeric
int	getInteger()	5	numeric
long	getLong()	6	numeric
float	getFloat()	7	numeric
date	getDate()	8	date
text	getString()	9	string	>3.5.5
time	getTime()	10	string	>3.5.8

In the props file one lists now the type names that the database returns and what Java type it represents (via the identifier), e.g.:

CHAR=0
VARCHAR=0

CHAR and VARCHAR are both String types, hence they are interpreted as String (identifier 0)

Note: in case database types have blanks, one needs to replace those blanks with an underscore, e.g., DOUBLE PRECISION must be listed like this:

DOUBLE_PRECISION=2

See also

• Databases
• Properties File