Correction of step descriptions

docs/manual/developer/07_understanding_build_system.md

@@ -125,15 +125,45 @@ module located under `ssg/`.
 
 ## How OVAL is Built
 
-Creating OVAL checks is done in two steps.
-First, all available OVAL checks are combined into a one unlinked OVAL document.
-The OVAL shorthands are loaded into the OVAL Document object and, in the case of template shorthand, extended using jinja macros before loading.
+The build of the OVAL document takes place in two steps.
+
+### 1. Combination of OVALs
+
+In the first step, all available and applicable OVAL checks are built into a single unlinked OVAL document stored in the `build/${PRODUCT}/oval-unlinked.xml` directory.
+The `oval-unlinked.xml` document is generated using the `combine_ovals.py` script.
+The OVAL shorthands are loaded into the OVAL Document object in the order that the benchmark checks are loaded first, followed by the shared directory checks.
 If the shorthand is already loaded into the OVAL Document object, it is skipped.
-Shorthands are loaded in the order that benchmark checks are loaded first, followed by shared directory checks.
-
-The second step is to link the generated document from the previous step with the XCCDF document.
-The unlinked OVAL document is loaded into the OVAL Document object while the XML file is being loaded into the object instance.
-Validation of the OVAL document is performed during and after loading (for example, whether all the checks listed in the XCCDF are present in the OVAL document).
-After validation of the OVAL document, the IDs are converted to valid OVAL IDs.
-The OVAL document is then saved as an XML file. During saving, a minimal OVAL document is generated for each rule as an artifact.
-The last step is to link the file to the XCCDF document.
+
+Steps of loading the OVAL shorthand:
+
+1. The OVAL Shorthand file is loaded as a string, and in the case of not templated Shorthand, it is expanded using Jinja macros before loading.
+2. The OVAL Shorthand string is processed by the OVAL Document object.
+   1. The OVAL Shorthand string is loaded into the OVAL Shorthand object.
+   2. The OVAL Shorthand object is validated.
+      The following properties are checked:
+       - Whether the OVAL definitions are applicable to the product.
+       - If there is an OVAL definition in the shorthand with the same id as the given rule_id.
+3. If the OVAL Shorthand object is valid, it is added to the OVAL Document object.
+
+After all OVAL Shorthands are loaded, the affected platforms of the loaded OVAL definitions are completed.
+And then the OVAL document is saved as an XML file in `build/${PRODUCT}/oval-unlinked.xml`.
+
+### 2. Linking OVAL Document
+
+The second step is performed when building an XCCDF document using the `build_xccdf.py` script.
+In this step, the `oval-unlinked.xml` document from the previous step is linked (IDs between rules and checks are aligned) to the XCCDF document being built.
+
+Steps to link an OVAL document to an XCCDF document:
+
+1. The unlinked OVAL document `oval-unlinked.xml` is loaded into the OVAL Document object.
+2. The integrity of the references to the components of the OVAL Document object is verified.
+3. For each XCCDF rule that has a CCE identification and
+   has an OVAL check implemented, a new `<reference>` element with the CCE ID is added to the OVAL definition.
+4. The OVAL definition referenced by the XCCDF is checked to be defined in the OVAL document.
+5. Verify if `<xccdf:Value>` `type` to corresponding OVAL variable `datatype` export matching [constraint](http://csrc.nist.gov/publications/nistpubs/800-126-rev2/SP800-126r2.pdf#page=30&zoom=auto,69,313) is met.
+   Also correct the `type` attribute of those `<xccdf:Value>` elements where necessary in order the produced content to meet this constraint.
+6. Verify that the referenced CCE identifiers are correct.
+7. Translate the identifiers in the OVAL Document object using `IDTranslator`.
+8. The OVAL Document object is stored as an XML file `build/ssg-${PRODUCT}-oval.xml`.
+9. For each XCCDF rule, a minimal OVAL Documents document is generated as an artifact
+10. For each reference of OVAL check in XCCDF, a link to the `check-content` and a `check-export` element is added.