There are three different ways to declare your XSDs. It does not matter which way you choose, or how you combine them, as long as the XSD Adapter can find all needed schemas.
Within the Workflow: 
        org.eclipse.xtend.typesystem.xsd.XSDMetaModel  can have any
        amount of schemaFile elements.
<component class="org.eclipse.xtend.typesystem.xsd.XMLReader">
  <modelSlot value="model" />
  <uri value="${file}" />
  <metaModel id="mm" class="org.eclipse.xtend.typesystem.xsd.XSDMetaModel">
    <schemaFile value="model/loadcurve.xsd" />
    <schemaFile value="model/device.xsd" />
  </metaModel>
</component>
Within the XML file: XML files can contain
        schemaLocation attributes which associate the
        schema's namespace with the schema's filename. If the schema is
        created using WTP like described in the section called “Step 3: Create a Model using XML” , the
        schemaLocation attribute is created
        automatically.
<?xml version="1.0" encoding="UTF-8"?> <device:Device xmlns:device="http://www.eclipse.org/modeling/xpand/example/model/device" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.eclipse.org/modeling/xpand/example/model/device device.xsd"> <device:Name>MyLaptop</device:Name> </device:Device>
Within an XSD: If one schema imports another, the
        import element can have a
        schemaLocation attribute, too.
<?xml version="1.0" encoding="UTF-8"?>
<schema
  targetNamespace="http://www.eclipse.org/modeling/xpand/example/model/device"
  elementFormDefault="qualified" xmlns="http://www.w3.org/2001/XMLSchema"
  xmlns:tns="http://www.eclipse.org/modeling/xpand/example/model/device"
  xmlns:lc="http://www.eclipse.org/modeling/xpand/example/model/loadcurve"
  xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore">
  <import
    namespace="http://www.eclipse.org/modeling/xpand/example/model/loadcurve"
    schemaLocation="loadcurve.xsd">
  </import>
  <complexType name="Device">
    <sequence>
      <element name="Name" type="string" />
      <element name="LoadCurve" type="lc:LoadCurve" />
    </sequence>
  </complexType>
  <element name="Device" type="tns:Device"></element>
</schema>