Joomla 1.5 does not provide an upgrade path from earlier versions. Converting an older site to a Joomla 1.5 site requires creation of a new empty site using Joomla 1.5 and then populating the new site with the content from the old site. This migration of content is not a one-to-one process and involves conversions and modifications to the content dump.
An automated method of migration has been provided which uses a migrator component to create the migration dump out of the old site (Mambo 4.5.x up to Joomla 1.0.x) and a smart import facility in the Joomla 1.5 Installation that performs required conversions and modifications during the installation process. Migration can be performed manually. This involves exporting the required tables, manually performing required conversions and modifications and then importing the content to the new site after it is installed. Automated migration
This is a two phased process using two tools. The first tool is a migrator component named ‘com_migrator’. This component has been contributed by Harald Baer and is based on his ‘eBackup’ component. The migrator needs to be installed on the old site and when activated it prepares the required export dump of the old site's data. The second tool is built into the Joomla 1.5 installation process. The exported content dump is loaded to the new site and all conversions and modification are performed “on-the-fly
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