<s:complexType name="ServerSyncUpdateData">
     <s:element minOccurs="0" maxOccurs="1" name="Id" 
     type="s1:UpdateIdentity" />
     <s:element minOccurs="0" maxOccurs="1" 
     name="XmlUpdateBlob" type="s:string" />
     <s:element minOccurs="0" maxOccurs="1" 
     type="s1:ArrayOfBase64Binary" />
     <s:element minOccurs="0" maxOccurs="1" 
     type="s:base64Binary" />

Id: This field MUST be present. It identifies the update revision that is described in this structure. The details of UpdateIdentity are specified in section

XmlUpdateBlob: This field MUST be present if XmlUpdateBlobCompressed is absent. This field MUST be absent if XmlUpdateBlobCompressed is present. The field contains the metadata associated with the update.

FileDigestList: Contains an array of file digests, one for each content file associated with the update revision. The file digest is an SHA-1 hash of the content of the file. If the update revision does not have any associated content file, this field MUST be absent.

XmlUpdateBlobCompressed: This field MUST be absent if XmlUpdateBlob is present. It contains metadata associated with the update, compressed using a LZX variant of the Lempel-Ziv compression algorithm. For more information, see [MSDN-CAB]. The LZX window size used for compressing this field is 2 megabytes.