fix isvalid function in query data set

chapter_3/create_dataset/query.rst

@@ -3,7 +3,7 @@ SQL Query Data Set
 
 Selecting the query option requires the BI developer to write an SQL statement to retrieve data.
 
-Pay attention that the SQL dialect depends on the chosen data source. The SQL text must be written in the Query text area. Look at this SQL query example.
+Remember that the SQL dialect depends on the data source that has been chosen. The SQL text must be written in the Query text area. Below a SQL query example.
 
 .. code-block:: sql
          :caption: SQL query example
@@ -14,7 +14,7 @@ Pay attention that the SQL dialect depends on the chosen data source. The SQL te
           JOIN promotion p on s.promotion_id=p.promotion_id
           GROUP BY p.media_type
 
-It is also possible to dynamically change the original text of the query at runtime. This can be done by defining a script (Groovy or JavaScript) and associating it to the query. Click on the **Edit Script** section (see next figure) and the script editor will open. Here you can write the script. The base query is bounded to the execution context of the script (variable query) together with its parameters (variable parameters) and all the profile attributes of the user that executes the dataset (variable attributes).
+It is also possible to dynamically change the original text of the query at runtime. This can be done by defining a script (Groovy or JavaScript) and associating it to the query. Click on the **Edit Script** section (see next figure) to open the script editor and write your script. The base query is bounded to the execution context of the script (variable query) together with its parameters (variable parameters) and all the profile attributes of the user that executes the dataset (variable attributes).
 
 .. _scripteditingdataset:
 .. figure:: media/image31.png
@@ -28,11 +28,11 @@ In the script below we use JavaScript to dynamically modify the ``FROM`` clause
          :linenos:
 
           if(isValid('year')) {		  
-		          if( parameters.get('year') == 1997 ) {
+		    if( parameters.get('year') == 1997 ) {
                   query = query.replace('FROM sales_fact_1998', 'FROM sales_fact_1997');
               } else { 
                   query = query; // do nothing
               }
             }	  
 
-In the above example we use the function *isValid* to test if the parameter value contains a not null value.
+In the above example we use the function *isValid* to test whether the parameter *year* contains a *null* value or not.