Add README.md fileandroid-q-preview-1

To explain the add and remove scheam, README.md file is added.

Bug: 80453829
Test: check in go/marked
Change-Id: I2785dde507b9d79ba1f12b6797a9254e63caba5c

1 files changed, 178 insertions, 0 deletions

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+# ConfigFile as API
+
+The ConfigFile as API is a formal Treble interface describing schemas of
+configuration files used across system and vendor partitions.
+The Java APIs in the current.txt file are not Java APIs for apps. It's a proxy
+for the schema of a xml file used between the system and vendor partition.
+The xml files are only ever parsed by apps on the system partition.
+
+## Add Schema
+Add the schema (attribute, element or new complexType …) you want to add to the
+xsd file.
+
+#### before
+```xml
+<xs:element name="class">
+  <xs:complexType>
+    <xs:sequence>
+      <xs:element name="student" type="xs:string"/>
+    </xs:sequence>
+    <xs:attribute name="name" type=”xs:string”/>
+  </xs:complexType>
+</xs:element>
+```
+
+#### after
+```xml
+<xs:element name="class">
+  <xs:complexType>
+    <xs:sequence>
+      <xs:element name="student" type="xs:string"/>
+    </xs:sequence>
+    <xs:attribute name="name" type=”xs:string”/>
+    <xs:attribute name="number" type="xs:int"/>
+  </xs:complexType>
+</xs:element>
+```
+
+Then run "make {xsd_config module_name} .docs-update-current-api" or "make
+update-api" to update all the xsd_config modules.
+
+In the above example, two functions are added as below.
+* method public int getNumber();
+* method public void setNumber(int);
+
+## Remove Schema
+To remove a tag, add an annotation tag with the name of "Deprecated" into the
+tag to be deleted. Partners are not allowed to create new vendor images using
+deprecated tags
+
+#### before
+```xml
+<xs:element name="class">
+  <xs:complexType>
+    <xs:sequence>
+      <xs:element name="student" type="xs:string"/>
+    </xs:sequence>
+    <xs:attribute name="name" type=”xs:string”/>
+  </xs:complexType>
+</xs:element>
+```
+
+#### after
+```xml
+<xs:element name="class">
+  <xs:complexType>
+    <xs:sequence>
+      <xs:element name="student" type="xs:string">
+        <annotation name=”Deprecated”/>
+      </xs:element>
+    </xs:sequence>
+    <xs:attribute name="name" type=”xs:string”/>
+  </xs:complexType>
+</xs:element>
+```
+
+After adding “Deprecated” annotation, we need to update the api or schema just
+like when adding a tag. In the above example, a @Deprecate annotation is added.
+* method @Deprecated public java.util.List<java.lang.String> getStudent();
+After 2 years we can delete the tag. When deleting, delete the tag in the xsd
+file and the api in last_current.txt, and update it.
+
+## Release Schema
+If there are any changes, we update last_current.txt and last_removed.txt before
+release by copying current.txt and removed.txt to last_current.txt and
+last_removed.txt.
+
+## Supported/Unsupported Tags
+Only the follow tags and attributes are allowed:
+
+#### Supported
+```xml
+"xsd:schema" [
+]
+
+"xsd:element" [
+    "xsd:name" {
+        values: any valid java name
+    }
+    "xsd:type" {
+        values: built-in data type, simpleType or complexType
+    },
+    "xsd:ref" {
+        values: another element
+    },
+    "xsd:minOccurs" {
+        values: [ 0, maxOccurs ]
+    },
+    "xsd:maxOccurs" {
+        values: [ 1, unbounded ]
+    },
+]
+
+"xsd:attribute" [
+    "xsd:name" {
+        values: any valid java name
+    }
+    "xsd:type" {
+        values: built-in data type, simpleType or complexType
+    },
+    "xsd:ref" {
+        values: another element
+    },
+]
+
+"xsd:complexType" [
+    "xsd:name" {
+        values: any valid java name
+    }
+]
+
+"xsd:complexContent" [
+]
+
+"xsd:simpleContent" [
+]
+
+"xsd:restriction": [
+    "xsd:base" {
+        values: built-in data type
+    }
+]
+
+"xsd:extension": [
+    "xsd:base" {
+        values: built-in data type, simpleType or complexType
+    }
+]
+
+"xsd:simpleType": [
+    "xsd:name" {
+        values: any valid java name
+    }
+]
+
+"xsd:list": [
+    "xsd:itemType" {
+        values: built-in data type, or simpleType
+    }
+]
+
+"xsd:union": [
+    "xsd:memberTypes" {
+        values: built-in data type, or simpleType
+    }
+]
+
+"xsd:sequence": [
+]
+
+"xsd:choice": [
+]
+
+"xsd:enumeration": [
+    "xsd:value" {
+        values: built-in data type
+    }
+]
+```