Update README.md

README.md

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 # Version3SqlDataExtraction
-This repository contains SQL code to generate the LocalPatientData.csv and SharedAggregateData.csv files for 4CE Version 3.
+
+This repository contains SQL scripts to generate the LocalPatientData.csv and SharedAggregateData.csv files for 4CE Version 3.
+
+**IMPORTANT**: 4CE sites are not expected to run these scripts yet. We are providing the scripts so that sites can preview them and offer feedback and suggestions. Additional clinical variables (Common Data Elements, or CDEs) will be added to the scripts before they are finalized.
+
+
+## Introduction
+
+
+Thes SQL scripts in this repository generate a database table named FourCE_LocalPatientData. This table contains, in one location, all the data needed for 4CE studies. It is based on the i2b2 observation_fact table, where each row represents a clinical "observation" of a patient. The table is exported to a comma separated values (CSV) file named LocalPatientData.csv, which is used by 4CE R scripts. Never share this file outside your institution!
+
+The SQL scripts also (1) maps local codes in your database to standard 4CE comon data elements (CDEs); (2) selects groups of patients relevant to 4CE studies (e.g., patients with COVID-19); (3) randomly samples subsets of those patients for analysis; and (4) creates a summary table (FourCE_SharedAggregateData) with aggregate counts and statistics about the types of data that were collected.
+
+The current SQL scripts are written for Microsoft SQL Server and optimized for the i2b2 data model. However, there will also be an Oracle version of the final scripts. A set of OMOP-to-i2b2 database views will also be available to assist sites using the OMOP data model.
+
+
+## Instructions
+
 
 The MSSQL folder contains scripts for Microsoft SQL Server.
 
 STEP 1:
 
 Run the following scripts, which create stored procedures:
+
 1) 4CE_CreateTables
 2) 4CE_InsertCodeMappingsData ***
 3) 4CE_InsertSamplingGroupsData