added further specification of MapReduce role in the project in ch 4

document/chapters/chapter_4/chapter_4.tex

@@ -1,5 +1,7 @@
 \chapter{The MapReduce paradigm}
-This short chapter discusses the MapReduce paradigm, concluding the overview of the problem before exploring the solution proposed by this work. Firstly, a definition and the history of such paradigm will be provided. Then, the programming model will be discussed, explaining the basic concepts needed to utilize MapReduce; following that, an overview of the master-slave architecture is provided. Continuing the chapter, in an attempt to clarify as much as possible how the actual execution of a program that employs MapReduce works, an easy example of a MapReduce computation is displayed. To conclude this chapter, an analysis of the execution flow is presented.
+As previously discussed, Grid computing is a multipurpose tool aimed to offer devices' resources to perform various types of tasks. This project, despite being multipurpose in nature itself (meaning that organizes its structure keeping in mind the possibility to support additional services in the future), aims to specifically offer to a user the execution of a MapReduce service over the Grid.
+
+Hence, this short chapter discusses the MapReduce paradigm, concluding the overview of the problem before exploring the solution proposed by this work. Firstly, a definition and the history of such paradigm will be provided. Then, the programming model will be discussed, explaining the basic concepts needed to utilize MapReduce; following that, an overview of the master-slave architecture is provided. Continuing the chapter, in an attempt to clarify as much as possible how the actual execution of a program that employs MapReduce works, an easy example of a MapReduce computation is displayed. To conclude this chapter, an analysis of the execution flow is presented.
 
 \input{document/chapters/chapter_4/sections/1_definition_and_history.tex}
 \input{document/chapters/chapter_4/sections/2_programming_model.tex}