美國留學生項目管理專業畢業dissertation格式模板下載-Schedule Management & Control

工作分解結構（WBS）是工作內容的分層表示。它被證明是有效的，使用WBS的定義和結構工程。WBS現在是項目管理中的一個共同的工具，項目管理知識的書（PMBOK）收集和重新定義它的話。根據PMBOK的描述，WBS是一個可交付成果導向的層次分解的工作將由項目團隊執行（PMI，2008）。通過項目WBS，又可細分為更小的部分，為了讓項目經理或其他人員對項目要素明確。同時，它可以使操作程序標準化的一大貢獻。

在1917年由亨利·勞倫斯·甘特發明的甘特圖。甘特圖的形式是一種棒圖。以棒圖，橫軸表示的持續時間，而垂直軸代表在項目中的那些任務。在圖表中的單杠，給人以視覺上的形象，以饗讀者了解每個任務的條件。單杠的長度可以顯示的任務應該花多長時間的酒吧的開始和結束的時間點的任務的開始和結束。甘特圖是由任務持續時間的關系附件和時間尺度。

3. Overview of Schedule Management Tools

3.1 Work Breakdown Structure (WBS)
Work breakdown structure (WBS) is a hierarchical representation of the work contents. It is proved to be efficient that using WBS to define and structure the project works. WBS for now is a common tool in project management as the Project Management Book of Knowledge (PMBOK) collected the word and redefined it. According PMBOK’s describe, WBS is a deliverable oriented hierarchical decomposition of the work to be executed by the project team (PMI, 2008). Through WBS, the project can be subdivided into smaller parts in order to let project managers or other workers clear about the components of the project. And also, it can make a great contribution to operate procedure standardization.

The importance of Work Breakdown Structure has been acknowledged by both theoretical researchers and engineering practice personnel. First of all, tt is the basis for defining work packages which is the crucial work of project management preparation (Rad, 1999; Colenso, 2000). Garcia-Forniels et al. (2003) declared that the WBS is the most important tool for project management because it provides a basis for scheduling, planning, responsibility assignment, information management and control. Also, through the procedure of WBS, the construction project information can be collected by the computer. Thus the WBS is the fundamental of project informationize.

Being a kind of scientific methodology of project management, the process of decomposition lead by WBS is not arbitrary but according to a sequence of principles and standards. There are 3 most important pre-works need to complete before project managers initiate the WBS process. The first relates to the decomposition criteria, which reflect the facets of information by which the work is subdivided across the WBS hierarchy. The second is the sequencing of these criteria, which relates to the order in which the criteria are applied in the hierarchy. The third issue relates to the level of detail, which reflects the extent to which the entire work is decomposed.#p#分頁標題#e#

Meanwhile, there are another 3 principles should be followed:
1) Each hierarchy should be a complete reflection of the whole project.
2) Different hierarchy should have different standard when decomposition.
3) The amount of hierarchies should stay at a proper level that those tasks in the lowest hierarchy can be precisely evaluated.

3.2 Gantt Chart
Gantt chart is invented by Henry Laurence Gantt in 1917. The form of Gantt chart is a kind of bar diagram. In the bar diagram, the horizontal axis represents for the duration and the vertical axis represents for those tasks in the project. The horizontal bar in the chart gives a visual image to readers to understand the condition of each task. The length of the horizontal bar can show how long the task should spend; the start and the end of the bar represent the time point of the task starts and ends. Gantt chart is composed by task duration, line of relationship attachment and time scale.

Gantt chart is used widely in project management. According to the describe of Gantt chart which is stated before, the biggest usage of Gantt chart is that it can provide an overview of the project activities and their inner relationships and then to make a plan. Furthermore, using Gantt chart can also make analysis about the whole schedule plan, such as critical path calculation and total duration evaluation. In project operation stage, Gantt chart is also a useful tool in order to draw a clear conclusion about the deviation between the planned schedule and the recent one. To identify this kind of deviation is the foundation of adjustment, so as to keep the project run to the right way.

Compared with other schedule plan techniques such as PERT, there are several benefits when using Gantt chart. First of all, when dealing with small and medium sized projects, it can provide an excellent graphic image which is much easier to understand. Second, Gantt chart can be supported by some special project management software to realize complex calculations and complex dependencies and conduct “what-if” analysis (Harvey, 2011).

However, as a kind of primary project management tool which is developed for such a long time, Gantt chart has some limitations when dealing with complex problems. Especially for this modern society, more and more complex projects appeared. They are often considerably more complex than can be communicated effectively by a Gantt chart. Moreover, Gantt chart only represents few parts of project management field. It mainly focuses on schedule management but according to PMBOK, project management is composed by nine parts. And there are some researchers argued that Gantt chart do not represent the size of the project or the relative size of work elements, therefore the magnitude of a behind-schedule condition can be easily misunderstood (Stephen, 2011).

3.3 Program Evaluation and Review Technique (PERT)
Program Evaluation and Review Technique (PERT) is a kind of useful technology which is used in schedule planning and optimizing. It is developed in the late 1950’s for the US Navy’s Polaris project which had thousands of contractors. Based on the duration and the precedence relationship of those tasks, it can optimize the total duration and make a proper arrangement about each task’s position in the whole schedule plan.#p#分頁標題#e#

PERT is focus on the mile stone task (or time point) and the critical path which is consisted of a series of tasks that direct related to the total duration. The mile stone event represents some key points in schedule management that in these key points, to compare with the planed performance and the real one will let the project manager know exactly the project’s progress and potential risks. Those tasks in critical path should not be changed easily because a slight change will cause the whole schedule plan facing readjust risk. Of course on the other hand, to short the duration of tasks in critical path is the only way to short the whole duration of project. In addition, it should be stated that not like the Gantt Chart, those task durations in PERT are all expected value but not a precise pre-evaluation. So, the real value of duration is uncertain which means in the project management practice (Maria etc., 2011), readjustment should be considered first in the schedule planning.

PERT consists of several steps to complete a project plan. First of all, and also the fundamental of PERT process is to identify specific activities, the inner relationships between each tasks and milestones. This step is always done by WBS. The second step is to construct a network diagram. It has two major methods, Activity on Node method (AON) and Activity on Arrow method (AOA). AON method use nodes to represent tasks and arrows represent precedence relationships only. AOA method use arrows to represent tasks and the position of arrows represent precedence relationship. The next step is to estimate the time coefficients of each task. The time coefficients mainly include ES (earliest start time), EF (earliest finish time), LS (latest start time), LF (latest finish time), FF (free float) and TF (total float). The forth step is to determine the critical path. Commonly those tasks with zero free float are in the critical path. The last step is to update as project progresses. As it is stated before, the expected value of duration will be replaced by the real one in project management practice, so the PERT chart should be modified to cope with the new situation.

The benefits brought by PERT is obvious:
1) PERT promotes identification of the critical path and makes this visible for managers.
2) PERT promotes identification of late start, early start, and slack (free float and total float) for each task.
3) a PERT chart exactly defines and makes visible precedence relationships between the tasks identified by WBS.
4) PERT provides for potentially reduced project duration due to better understanding of precedence relationships leading to improved overlapping of tasks where feasible.

And also, there are some limitations exist when using PERT chart:
1) The accuracy of PERT is mainly based on the task identification which is done by WBS and the estimation of task duration. However, there can be potentially hundreds or thousands of activities and individual dependency relationships which can have large influence on the result of PERT chart.#p#分頁標題#e#
2) The lack of accurate timeframe on most PERT charts makes it harder to show status. And furthermore, some experts said that PERT over emphasized the critical path (Davaadorjin, 2010).
3) Just like Gantt chart, when the PERT charts become unwieldy, they are no longer used to manage the project.

. Task Identity by WBS
4.1 Decomposition Criteria
The set of decomposition criteria is the first difficult task when using WBS. In order to standardize the business process of WBS in construction area, a lot of organizations and individual researchers put forward their thoughts. The International Organization for Standardization (ISO, 1994) identified eight factors of classification for construction information. These include space (office spaces, recreational, etc.), facility (school, hospital, etc.), work section (masonry, concrete work, etc.), element (floors, stairs, etc.), construction aid (scaffolding, formwork, etc.), construction product (cement, paint, etc.), management (procurement, drawing, etc.) and attributes (size, shape, etc.). These facets were updated in ISO (2001) to include more classes. The ones relevant to this study are construction complexes (industrial complex, transport complex, etc.), construction entities (bridges, buildings, etc.), life cycle phases (production phase, design phase, etc.) and work results (filling, excavation, etc.).