You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: A review on integrated process planning and scheduling 
Chapter Title:  Integration models of IPPS 
1. Abstract of Cited Paper (BIB001):  Automated process planning (APP) has received a considerable amount of attention in recent years. This has mainly been due to APP allowing for the bridging of the gap between design and manufacturing, and for its automation of the related tedious human task. While there have been several efforts in developing interfaces between computer-aided design (CAD) and APP, little attention has been given to the integration of APP and scheduling, which is likely to be of even higher importance. This paper addresses the basic issues involved in the integration of the two functions, demonstrates a methodology and the potential benefits of the integrated approach by an example, and presents directions for future research. 
2. Abstract of Cited Paper (BIB002):  Summary Functional integration has taken the foreground in the current manufacturing system development. Process planning and job shop scheduling are two main manufacturing functions involved in shop floor activities. An integrated process planning model (IPPM) is introduced in this paper. The two functions (process planning and job shop scheduling) are truly integrated by means of distributed approach which is different from current nonlinear and alternative process planning approaches. In this paper, the two functions are integrated at task stage, while the nonlinear and alternative approaches are taken place at result stage which cannot be considered as real integration but rather interface. The introduced IPPM works in three levels, based on manufacturing resource availability and real time feedback from shop floor, they are pre-planning, pairing planning, and final planning. The IPPM consists of three modules, introduced in detailed in the paper, they are: process planning module, production scheduling module, and decision making module. An example is provided to illustrate the model. This paper is to be considered as a contribution to the research efforts in process planning and integrated manufacturing. 
3. Abstract of Cited Paper (BIB003):  Abstract Integration is often considered to be a tangible word. In fact integration is diffuse: it does not express in any detail how to conduct integration initiatives. On the other hand, integration docs represent a very efficient way of improving the operational characteristics of a manufacturing facility. The concepts provided for integration are derived from the discovery of time-dependent tasks within the process planning domain. When operating in dynamic environments it is important to separate static and dynamic controlled decision making and to provide architectures capable of providing the required dynamic knowledge at the time when the decisions are made. A natural expansion of this hypothesis is the development of an approach for process planning conducted concurrently with the other engineering activities within product life. This article introduces a practical approach to the integration of process planning and production control business functions. The approach outlines systematic methods t... 
4. Abstract of Cited Paper (BIB004):  In recent years, a few researchers have addressed the need for the integration of process planning and scheduling functions in order to achieve superior overall system performance. Many of these researchers have discovered that the potential savings are substantial when process planning and scheduling are integrated. It has been reported that typical scheduling objectives, such as minimizing makespan, maximizing equipment utilization, etc, can be significantly improved as the result of integration of these two important manufacturing system functions. In this paper, we present a review of the reported research in this area, discuss the extent of applicability of various approaches, and suggest directions for future research. 
5. Abstract of Cited Paper (BIB005):  Today’s manufacturing systems are striving for an integrated manufacturing environment. To achieve truly computer-integrated manufacturing systems (CIMS), the integration of process planning and production scheduling is essential. This paper proposes a framework for integration of process planning with production scheduling in a job shop environment for axisymmetric components. Based on the design specifications of incoming parts, feasible process plans are generated taking into account the real time shop floor status and availability of machine tools. The scheduling strategy prioritizes the machine tools based on cost considerations. 
6. Abstract of Cited Paper (BIB006):  Process planning and scheduling are considered as two separate and distinct phases in manufacturing. Traditional approaches to these problems do not consider the constraints of both domains simultaneously and can only result in sub-optimal solutions. This separation becomes a barrier to further improving manufacturing performance. Most process planning and scheduling systems are off-line and centralized. The process plans generated off-line may become invalid at the time of plan execution. On the other hand, scheduling based on rigid process plans may have already lost the optimal options. Today, there is an increasing need for the integration of process planning and scheduling to generate more realistic and practical solutions. This paper provides a literature review on the integration of process planning and scheduling, particularly on agent-based approaches. It is followed by an overview of our approach toward distributed process planning and scheduling. The paper is finally concluded with future research opportunities.

Literature Review:
In the early studies of CIMS, it has been identified that IPPS is very important to the development of CIMS BIB005 BIB006 . The preliminary idea of IPPS was first introduced by BIB001 , and  .  used alternative process plans to improve the flexibility of manufacturing systems. BIB002 introduced the concept of dynamic feedback into the IPPS. The integration model proposed by BIB003 and BIB004 extended the concepts of alternative process plans and dynamic feedback and defined an expression to the methodology of hierarchical approach. Some earlier works of the integration strategy had been summarised in BIB005 , and BIB007 . In recent years, in the area of IPPS, some integration models have been reported and several implementation approaches have been employed. Many models of IPPS have been proposed, and they can be classified into three basic models based on IPPS: Non-linear Process Planning (NLPP)  , Closed-Loop Process Planning (CLPP) BIB002 and Distributed Process Planning (DPP) BIB003 BIB004 .