Answers:

1. Logs and its relationship with production orders
 
Logs are collection of changes that were recorded at various stages of progress. Messages that are generated whenever an event occurs with in or with respect to a production order are displayed and some times recorded in the logs of a production order. Some examples for events include creation, release, scheduling, costing, availability checks, status changes, deliveries etc. The above are some of the examples that occur with in a production order. There are other log messages which are displayed when events related to the production order occur.
 
Not all messages generated during the process of production order creation, maintenance or progresses are recorded in the logs. Some messages are temporary and will be stored only as long as the order is saved. While some are permanently recorded. Configuration settings are available to decide on whether certain messages are to be stored or not.
 
Please remember that Production order is a complex process linking various departments like BOM from design, Routing from planning, GI from stores, Confirmation from Production, stage inspection from QM, Sub contracting process, GR against production order, order completion ......... etc. Any change in any one of the process or component or schedule generates an enormous amount of changed data. So SAP does not store all changes. This is one way of saving precious storage space.
 
2. Read PP Masters: 
 
A production order is created by logically combining BOM and routing. If any change is made in either of the two or both the master data, such changes (latest changes) can be updated to the current production order by way of "Read PP Master". With in "Read PP Master" you have the option of selecting whether BOM or Routing is to be updated.
 
In case any GI or Operation confirmation or Pr is raised with respect to the production order, SAP will not allow changing master data by way of "Read PP Master". How ever you can reverse the GI or cancel the confirmation and execute "Read PP Master"  
 
3. Pegged requirements
 
When ever a component (material) requirement (need or consumption) is generated with respect to another material, a relation is established. This relation between the component and the material is called pegged requirement. Eg.: B is required to manufacture A. When a production order is created, B will be picked up from the BOM and a certain qty of B will be required to manufacture A. Here A is the pegged requirement of B. 

SAP PP Reference Books:
SAP Production Planning , Configuration, Interview Questions and Certification, Books

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