diff --git a/SDT/schema4.0/docs/SDT_JSON.md b/SDT/schema4.0/docs/SDT_JSON.md
index f48c352e71dfa3c561fe24135defe036f02f06a5..0b6c66bf7933db906f71224ea4013b2b11af4ad7 100644
--- a/SDT/schema4.0/docs/SDT_JSON.md
+++ b/SDT/schema4.0/docs/SDT_JSON.md
@@ -1,4 +1,8 @@
-JSON serialization is supported since SDT4.0 as it's very popular nowadays in the developers' communities, especially in the context of RESTful implementation. JSON is more concise and human-readable comparing to XML, but has less capability of formal schema definition and validation (such as the XML Schema as defined in [domain.xsd](SDT/schema4.0/src/domain.xsd)). 
+When SDT was introduced, XML was the favorite encoding format for schemas. Since then, JSON became more popular in the developers' communities, especially in the context of RESTful implementation. 
+
+JSON is more concise and human-readable comparing to XML, but has less capability of formal schema definition and validation (such as the XML Schema as defined in [domain.xsd](SDT/schema4.0/src/domain.xsd)). 
+
+For these reasons, JSON serialization is supported since SDT4.0.
 
 There are some open tools such as [JSON Schema](http://json-schema.org/) that might be useful for describing and validating the JSON serialization of SDT, but it's not yet a formal standard and is still under development.