please I need answers for these questions the book is System

please I need answers for these questions the book is Systems Analysis Design with UML v 2 Fourth Edition

Q1)- What is the relationship between level 0 and level 1 DFD diagrams? Explain.

Q2)- What does Use Case mean? and what does use case describe?

Q3)- What does triggers mean in use case, and what are the trigger types? and who\'s usually be a trigger?

Q4)- Describe the best way to validate the content of use cases.

Q5)- What is the purpose of an intersection entity? Describe the steps used to create an intersection entity?

Solution

R is an implementation of the S programming language combined with lexical scoping semantics inspired by Scheme.^[11] S was created by John Chambers while at Bell Labs. There are some important differences, but much of the code written for S runs unaltered.^[12]

R was created by Ross Ihaka and Robert Gentleman^[13] at the University of Auckland, New Zealand, and is currently developed by the R Development Core Team, of which Chambers is a member. R is named partly after the first names of the first two R authors and partly as a play on the name of S.^[14] The project was conceived in 1992, with an initial version released in 1995 and a stable beta version in 2000