<?xml version="1.0" encoding="utf-8"?>
<ManualTopic ID="/baanerp/tt/onlinemanual/vrm_vrc_derivation" xml:lang="en">
	<Header>
		<Title xmlns:HTML="http://www.w3.org/TR/REC-html40">VRC derivation</Title>
		<Keyword ContextSensitive="No"><Level1>Version and release management</Level1>
			<Level2>VRC derivation</Level2>
		</Keyword>
		<Keyword ContextSensitive="No"><Level1>VRC derivation</Level1>
		</Keyword>
	</Header>
	<GeneralSection><Paragraph class="Default">If a user starts a software component, for example a session, the Virtual Machine (VM) searches from the outside to the inside, as shown in the following figure. The Virtual Machine (VM) searches for any customizations on the component made by the customer in the own customization. If no own customizations exist, the Virtual Machine (VM) searches for a customer-specific customization, and so on.</Paragraph>
		<Figure space-and-orientation="indented-estimated"><FigIntro>The following figure shows how the Virtual Machine (VM) navigates through the customizations on a component.</FigIntro>
			<HTML:IMG width="358" height="331" SRC="../images/tr_graph_vrm_vrc_derivationa.gif" path="/enterpriseserver/tools/tt/onlinemanual" btb-count="1" btb-count2="1" btb-image-name="tr_graph_vrm_vrc_derivationa.gif" btb-source-path="C:\SVN\docnl\Technology\EnterpriseServer~8.5\EnterpriseServer" btb-image-path="/enterpriseserver/tools/tt/images/tr_graph_vrm_vrc_derivationa.gif" ID="IDAWLYBC" alt="[...]" xmlns:HTML="http://www.w3.org/TR/REC-html40"/><FigCaption>Navigation of the Virtual Machine (VM) through the VRC structure</FigCaption>
		</Figure>
		<Paragraph class="Default">The search path also depends on the <Link href="/baanerp/tt/glossary/glossary#000000000000012" role="glossary">package combination</Link> and company to which the user is linked. For example, the <Link href="/baanerp/tt/glossary/glossary#000000000000013" role="glossary" Update="No">package VRCs</Link> in a development package combination are derived from the VRCs in the run-time package combination, these run-time package combinations were, in turn, derived from standard package VRCs.</Paragraph>
		<Figure space-and-orientation="indented-estimated"><FigIntro>The following figure shows the derivation structure of the development package combination.</FigIntro>
			<HTML:IMG width="507" height="263" SRC="../images/tr_graph_vrm_vrc_derivationb.gif" path="/enterpriseserver/tools/tt/onlinemanual" btb-count="1" btb-count2="1" btb-image-name="tr_graph_vrm_vrc_derivationb.gif" btb-source-path="C:\SVN\docnl\Technology\EnterpriseServer~8.5\EnterpriseServer" btb-image-path="/enterpriseserver/tools/tt/images/tr_graph_vrm_vrc_derivationb.gif" ID="IDAHMYBC" alt="[...]" xmlns:HTML="http://www.w3.org/TR/REC-html40"/><FigCaption>Package VRC derivation structure</FigCaption>
		</Figure>
		<Paragraph class="Default">In this previous figure, the VRCs with customer extension dev are derived from the VRCs with the cus extension, which themselves are derived from standard VRCs. If a user works with package combination b61O_a_cus and starts a software component, the Virtual Machine (VM) searches for a customization in the VRC with the cus extension. If such a customization is found, this customized component is started. If no such customization exists, the component in the standard VRC is started.</Paragraph>
		<Paragraph class="Default">If a user works with package combination b61O_a_dev and starts a software component, the Virtual Machine (VM) searches for a customization in the VRC with the dev extension. If no such customization is found, the Virtual Machine (VM) continues the search in the cus VRC. If this VRC also does not contain a customized version of the component, the Virtual Machine (VM) starts the component in the standard VRC.</Paragraph>
		<Paragraph class="Default">If you create many package VRCs, derived from each other, the derivation structure can get complicated.</Paragraph>
		<List><ListIntro>The consequences of a cluttered and complicated VRC derivation structure are:</ListIntro>
			<ListItem>A decrease in system performance due to the longer derivation structure</ListItem>
			<ListItem>A cluttered directory structure due to a large number of newly-created package VRCs</ListItem>
		</List>
		<Paragraph class="Default">For this reason, you must regularly purge the VRC derivation structure. Before you can purge a package VRC, you must make sure that the VRC is not connected to a package combination. You can disconnect the package VRC from a package combination with the <Link href="/baanerp/tt/aad/ttaad1121m000" role="session">Packages by Package Combination (ttaad1121m000)</Link> session.</Paragraph>
		<Note><SectionTitle>
                                 Note
                              </SectionTitle>
			<Paragraph class="Default">If you purge a package VRC, the derived-from structure changes. The user files and fd6.2 files, for the involved users and package combinations, are automatically regenerated so that they contain the new derived-from structure.</Paragraph>
		</Note>
		<Figure space-and-orientation="indented-estimated"><FigIntro>The following figure provides an example of a package VRC derivation structure before and after the purge:</FigIntro>
			<HTML:IMG width="392" height="291" SRC="../images/tr_graph_vrm_vrc_derivationc.gif" path="/enterpriseserver/tools/tt/onlinemanual" btb-count="1" btb-count2="1" btb-image-name="tr_graph_vrm_vrc_derivationc.gif" btb-source-path="C:\SVN\docnl\Technology\EnterpriseServer~8.5\EnterpriseServer" btb-image-path="/enterpriseserver/tools/tt/images/tr_graph_vrm_vrc_derivationc.gif" ID="IDAYMYBC" alt="[...]" xmlns:HTML="http://www.w3.org/TR/REC-html40"/><FigCaption>Package VRC derivation structure before and after the purge procedure</FigCaption>
		</Figure>
		<Paragraph class="Default">Typically, only customer-defined VRCs are purged that contain customized software components that do not belong to a package combination. However, you can also purge the package VRCs that contain the standard software.</Paragraph>
		<Paragraph class="Default">For example, the following figure shows the derivation structure of the package VRCs that contain the standard software of the ERP LN Common package. A new standard can contain new functionality, feature packs, bug fixes, and so on.</Paragraph>
		<Paragraph class="Default">A new standard is put on top of its predecessor, so software components can be duplicated. Therefore, you must purge the standard package VRCs regularly to remove the duplications.</Paragraph>
		<Figure space-and-orientation="indented-estimated"><HTML:IMG width="214" height="291" SRC="../images/tr_graph_vrm_vrc_derivationd.gif" path="/enterpriseserver/tools/tt/onlinemanual" btb-count="1" btb-count2="1" btb-image-name="tr_graph_vrm_vrc_derivationd.gif" btb-source-path="C:\SVN\docnl\Technology\EnterpriseServer~8.5\EnterpriseServer" btb-image-path="/enterpriseserver/tools/tt/images/tr_graph_vrm_vrc_derivationd.gif" ID="IDAJNYBC" alt="[...]" xmlns:HTML="http://www.w3.org/TR/REC-html40"/><FigCaption>Derivation structure of the ERP LN Common package</FigCaption>
		</Figure>
		<Paragraph class="Default">The maximum VRC depth, in other words, the number of VRC that you can stack on top of each other, is 40 VRCs. However, for best results, keep the maximum VRC depth as low as possible.</Paragraph>
	</GeneralSection>
</ManualTopic>
