XSD file is broken and does not match the docs

[jtojnar]

Some are easy to fix, like the following but there are also references to missing elements and various wrong things like <pkgname> inside <component> instead of <components>.

--- a/data/appstream.xsd
+++ b/data/appstream.xsd
@@ -13,7 +13,8 @@
     <xsd:complexType mixed="true">
       <xsd:sequence>
         <xsd:element ref="id" minOccurs="1" maxOccurs="unbounded"/>
-        <xsd:element ref="pkgname" minOccurs="1" maxOccurs="1"/>
+        <xsd:element ref="metadata_license" minOccurs="1" maxOccurs="1"/>
+        <!-- <xsd:element ref="pkgname" minOccurs="1" maxOccurs="1"/> -->
         <xsd:element ref="name" minOccurs="1" maxOccurs="unbounded"/>
         <xsd:element ref="summary" minOccurs="1" maxOccurs="unbounded"/>
         <xsd:element ref="description" minOccurs="0" maxOccurs="1"/>
@@ -21,7 +22,7 @@
         <xsd:element ref="project_group" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="keywords" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="icon" minOccurs="1" maxOccurs="unbounded"/>
-        <xsd:element ref="appcategories"/>
+        <!-- <xsd:element ref="appcategories"/> -->
         <xsd:element ref="mimetypes" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="url" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="screenshots" minOccurs="0" maxOccurs="1"/>
@@ -29,26 +30,24 @@
         <xsd:element ref="releases" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="architectures" minOccurs="0" maxOccurs="1"/>
       </xsd:sequence>
-      <xsd:simpleContent>
-        <xsd:extension base="xsd:string">
-          <xsd:attribute name="type" use="optional">
-            <xsd:simpleType>
-              <xsd:restriction base="xsd:string">
-                <xsd:enumeration value="generic"/>
-                <xsd:enumeration value="desktop"/>
-                <xsd:enumeration value="codec"/>
-                <xsd:enumeration value="font"/>
-                <xsd:enumeration value="inputmethod"/>
-              </xsd:restriction>
-            </xsd:simpleType>
-          </xsd:attribute>
-        </xsd:extension>
-      </xsd:simpleContent>
+      <xsd:attribute name="type" use="optional">
+        <xsd:simpleType>
+          <xsd:restriction base="xsd:string">
+            <xsd:enumeration value="generic"/>
+            <xsd:enumeration value="desktop-application"/>
+            <xsd:enumeration value="codec"/>
+            <xsd:enumeration value="font"/>
+            <xsd:enumeration value="inputmethod"/>
+          </xsd:restriction>
+        </xsd:simpleType>
+      </xsd:attribute>
     </xsd:complexType>
   </xsd:element>
 
   <xsd:element name="id" type="xsd:string"/>
 
+  <xsd:element name="metadata_license" type="xsd:string"/>
+
   <xsd:element name="pkgname" type="xsd:string"/>
   <xsd:element name="name">
     <xsd:complexType>
@@ -191,24 +190,18 @@
     </xsd:complexType>
   </xsd:element>
   <xsd:element name="screenshot">
-    <xsd:complexType>
-      <xsd:simpleContent>
-        <xsd:extension base="xsd:string">
-          <xsd:attribute name="type" use="optional">
-            <xsd:simpleType>
-              <xsd:restriction base="xsd:string">
-                <xsd:enumeration value="default"/>
-              </xsd:restriction>
-            </xsd:simpleType>
-          </xsd:attribute>
-        </xsd:extension>
-      </xsd:simpleContent>
-    </xsd:complexType>
     <xsd:complexType mixed="true">
       <xsd:choice maxOccurs="unbounded" minOccurs="1">
         <xsd:element ref="image"/>
         <xsd:element ref="caption"/>
       </xsd:choice>
+      <xsd:attribute name="type" use="optional">
+        <xsd:simpleType>
+          <xsd:restriction base="xsd:string">
+            <xsd:enumeration value="default"/>
+          </xsd:restriction>
+        </xsd:simpleType>
+      </xsd:attribute>
     </xsd:complexType>
   </xsd:element>
   <xsd:element name="image">
@@ -223,8 +216,8 @@
               </xsd:restriction>
             </xsd:simpleType>
           </xsd:attribute>
-	  <xs:attribute name="width" type="xsd:positiveInteger" use="required"/>
-	  <xs:attribute name="height" type="xsd:positiveInteger" use="required"/>
+          <xsd:attribute name="width" type="xsd:positiveInteger" use="required"/>
+          <xsd:attribute name="height" type="xsd:positiveInteger" use="required"/>
         </xsd:extension>
       </xsd:simpleContent>
     </xsd:complexType>

[ximion]

That file is old and outdated (it has not been touched for 4 years) and I should likely just remove it. If you want to validate your metadata files, they way to do it is to use appstreamcli validate now.

[jtojnar]

Cool, that works much better than the validator from appstream-glib. Though a working schema is much more useful than just for validation – for example, I wanted to see what values can the <component>’s type attribute contain. I was curious about desktop vs desktop application, as it is not very clear from the docs.

[ximion]

Hmm, the specification should actionally mention that particular information... desktop is legacy but eternally supported, while desktop-application is the "new" thing. Since we will support both names forever, they are essentially aliases to one another.
See also the code for those enums: https://github.com/ximion/appstream/blob/master/src/as-component.c#L185-L268 (although to just get the values, looking at the API documentation is easier).