add model interaction

docs/about/history.md

@@ -15,6 +15,6 @@ However, in the progess of model expansion, many payroll tax featured developmen
 
 From the perspective of model management, many research organizations also build their tax model systems consisted of an income tax model and payroll tax model. It is thus considered better to have Tax-Calculator and Taxcalc-Payroll seperately serveing as income tax calculator and payroll tax calculator.
 
-Taxcalc-Payroll inherits the software infrastructure from Tax-Calculator. These two models are highly integrated, with most tax calaulation functions can be called by each other. Users can still conduct both income and payroll tax analysis from one either model.
+Taxcalc-Payroll inherits the software infrastructure from Tax-Calculator. These two models are highly integrated, with most tax calaulation functions can be called by each other. Users can still conduct both income and payroll tax analysis from either model.
 
 

docs/about/model_interaction.md

@@ -0,0 +1,10 @@
+Model Interaction 
+=======
+
+Taxcalc-Payroll is the microsimulation model conducting the static analysis of federal individual income and payroll taxes, it interacts with other models to conduct higher level analysis, like revenue estimation and non-static analysis. 
+
+Taxcalc-Payroll takes the input data (reweighted PUF and CPS data) from [Tax-Data](https://github.com/PSLmodels/taxdata) to conduct tax revenue estimation. Taxcalc-Payroll works with [Behavior Response Package](https://github.com/PSLmodels/Behavioral-Responses) to conduct the conventional analysis. 
+
+To be noticed, Tax-Calculator and Taxcalc-Payroll are highly integrated. Users can call most of Tax-Calculator's functions from Taxcalc-Payroll. This means the user can do both income tax and payroll tax analysis from the model. (this also holds for Tax-Calculator)
+
+Please refer to [AEI OSPC webpage](https://www.ospc.org/taxmodels/) for a more detailed documentation.

docs/index.md

@@ -46,10 +46,9 @@ The cross-model validation work with NBER's TAXSIM model is described
 
 ## A parallel project with Tax-Calculator
 
-Taxcalc-Payroll focuses on payroll tax analysis. It is a parallel project with Tax-Calculator 
-which aims to be focusing more on income tax analysis. Taxcalc-Payroll inherits the infrastructure 
-from Tax-Calculator. Two models are highly integrated. Users can do both income tax and payroll tax
- analysis in either of the model
+Tax-Calculator and Taxcalc-Payroll are the microsimulation models for income tax and paryroll tax analysis.
+They are parallel projects. Two models are highly integrated. Users can do both income tax and payroll tax 
+analysis from either model.
 
 Please read the details at {doc}`about/history`.