Operations Planning, Scheduling and Enterprise Systems

Introduction and Context

Operations planning translates an organization’s strategic intentions into coordinated decisions about demand, workforce, inventory, materials, capacity, equipment, and timing. In an entrepreneurial firm, planning is especially important because scarce cash, limited capacity, uncertain demand, and dependence on suppliers make operational mistakes costly. A promising product can fail commercially if it cannot be produced consistently, delivered on time, or supported with appropriate materials.

Planning occurs at several linked levels. Aggregate planning establishes broad production, workforce, inventory, and subcontracting decisions over a medium-term horizon. The master production schedule (MPS) converts the aggregate plan into specific end-item quantities and dates. Materials requirements planning (MRP) determines which components and raw materials are needed, in what quantities, and when orders or production should begin. Capacity requirements planning (CRP) tests whether the proposed schedule is feasible. Finally, detailed sequencing and scheduling assign jobs to resources in a practical order.

Enterprise resource planning (ERP) systems connect these activities through shared data and transaction processing. ERP does not replace managerial judgment; it provides an integrated information environment in which decisions can be based on consistent records.

Learning Objectives

By the end of this chapter, students should be able to:

1. Explain the hierarchy and purpose of aggregate planning, MPS, MRP, CRP, and detailed scheduling.
2. Construct and interpret a bill of materials and an MRP record.
3. Apply basic aggregate-planning and scheduling calculations.
4. Explain sequencing rules and evaluate their limitations.
5. Describe how ERP integrates operational information and identify implementation risks.
6. Analyze an operations-planning problem and recommend an appropriate response.

1. The Hierarchy of Operations Planning

Operations planning is hierarchical because decisions differ in time horizon, level of detail, and reversibility.

The hierarchy is not entirely one-directional. Capacity problems identified by CRP may require changes to the MPS, aggregate plan, or even product design. Similarly, supplier disruption or a large customer order may cause planners to revise several levels simultaneously.

A useful principle is that higher-level plans should constrain lower-level plans without prescribing every operational detail. Excessive detail too early creates false precision, while insufficient detail prevents execution.

2. Aggregate Planning

Aggregate planning balances expected demand and available resources for product families rather than individual stock-keeping units (SKUs). Its usual horizon is medium term. The planner may decide total production, workforce size, overtime, subcontracting, inventory, and backorders.

Three broad strategies are common:

• Level strategy: maintain a relatively stable production rate and workforce while using inventory or backorders to absorb demand variation.
• Chase strategy: vary production or workforce to follow demand closely, minimizing inventory but potentially increasing hiring, layoffs, training, and instability.
• Mixed strategy: combine regular time, overtime, inventory, subcontracting, temporary labor, and controlled backorders.

A simplified aggregate-planning cost model is:

Here, C_R is regular-time unit production cost, R is regular production; C_O and O are overtime cost and overtime production; C_I and I are inventory holding cost and ending inventory; C_B and B are backorder cost and ending backorders; C_S and S are subcontracting cost and subcontracted quantity; and C_H and H represent workforce-related costs. All terms must use compatible monetary units.

For each period, the fundamental flow relationship is:

If backorders are represented as negative inventory, the same equation can be used, provided the sign convention is applied consistently. The model is useful for comparing alternatives, but it may omit setup costs, minimum lot sizes, learning effects, service-level requirements, and labor regulations. Linear programming or spreadsheet optimization can support larger planning problems, but the resulting solution remains dependent on forecast quality and valid cost estimates.

Worked Example: Comparing Two Simple Plans

A firm forecasts demand of 400 units in month 1 and 600 units in month 2. It begins with zero inventory and wants zero ending inventory. Regular production costs £10 per unit, overtime costs £14, and inventory holding cost is £1 per unit per month.

Under a chase plan, production equals demand in each month: 400 regular units and 600 regular units. Production cost is:

1,000 × £10 = £10,000.

Under a level plan, the firm produces 500 units each month. Month 1 ends with 100 units of inventory, which are used in month 2. Production cost remains £10,000, but the 100 units held for one month add £100. Thus, the relevant cost is £10,100, assuming no capacity or workforce adjustment costs. The level plan is slightly more expensive in this simplified example but may be operationally preferable if stable employment, equipment utilization, or supplier orders are important.

3. Master Production Scheduling

The MPS specifies when particular finished products or major assemblies should be completed. It is more detailed than an aggregate plan but should not be confused with a final shop-floor schedule. The MPS commonly includes forecast demand, customer orders, projected available balance, and available-to-promise (ATP) inventory.

A simplified projected available balance is:

where PAB_t is projected available balance in period t, MPS_t is scheduled production, F_t is forecast demand, and O_t is booked customer orders. The use of max(F_t,O_t) is a common simplified convention; organizations may use different demand-commitment rules.

ATP estimates the quantity that can be promised to new customers. For the first MPS period, a common calculation is:

For later MPS receipt periods, ATP includes the current receipt and orders up to the next receipt. ATP is not simply total inventory; it must protect existing commitments and account for timing.

MPS quality depends on a realistic aggregate plan, accurate inventory records, reliable bills of materials, and disciplined treatment of changes. Frequent unplanned changes create nervousness: suppliers and work centers repeatedly alter orders, increasing expediting, shortages, and waste.

4. Bills of Materials

A bill of materials (BOM) is a structured list of all components, subassemblies, and quantities required to make one unit of a parent item. A single-level BOM lists immediate components; a multilevel BOM shows the product structure across several levels.

For example, one bicycle may require one frame, two wheels, one gear assembly, and one seat. Each wheel may require one rim, one tire, and one tube. A planning BOM must identify quantity per parent, unit of measure, lead time, engineering revision, and effective dates.

The total quantity of a component required for a planned quantity of finished goods is:

For a component used through multiple levels, quantities are multiplied along the relevant path. If each product requires two wheels and each wheel requires one tire, one product requires 2 × 1 = 2 tires. When a component has multiple parents, requirements from all paths are added.

BOM accuracy is operationally critical. An incorrect quantity causes systematic shortages or excess inventory. An obsolete revision can cause production of nonconforming goods. Engineering change control must therefore communicate effective dates and replacement relationships to purchasing, production, quality, and service functions.

5. Materials Requirements Planning

MRP is a time-phased method for planning dependent-demand items. Dependent demand is derived from the demand for another item, such as the demand for engines derived from the production schedule for vehicles. MRP generally uses four inputs:

1. The MPS for end items.
2. The BOM.
3. Inventory records, including on-hand balances, scheduled receipts, safety stock, and open orders.
4. Lead-time and lot-sizing information.

The standard MRP logic is:

1. Determine gross requirements from the parent schedule and BOM.
2. Subtract available inventory and scheduled receipts.
3. Add planned receipts according to the lot-sizing rule.
4. Offset planned receipts by lead time to obtain planned order releases.
5. Explode the releases down the BOM to calculate lower-level requirements.

A basic net-requirement calculation is:

The formula assumes that projected availability is measured before the planned receipt in period t. If inventory is already sufficient, the net requirement is zero. A planned order receipt is then determined by the lot-sizing rule. Under lot-for-lot sizing, the receipt equals the net requirement. Under a fixed-order-quantity rule, the receipt may be the smallest permitted multiple that covers the requirement.

Worked MRP Example

Suppose an MPS requires 50 finished units in week 4. Each finished unit requires two units of component A. Component A has 20 units on hand, no scheduled receipts, and a one-week lead time. No safety stock is required, and lot-for-lot sizing is used.

Gross requirement in week 4:

50 × 2 = 100 units.

Net requirement:

100 − 20 = 80 units.

Therefore, MRP plans an 80-unit receipt in week 4. Because lead time is one week, the planned order release is 80 units in week 3. This calculation assumes all 20 units of inventory are usable and that no other demand consumes them.

MRP is powerful for dependent demand but does not automatically guarantee feasible capacity, supplier reliability, or accurate execution. It is a planning logic, not a substitute for inventory discipline or production control.

6. Capacity Requirements Planning

CRP converts planned orders into required work-center capacity and compares that requirement with available capacity. It typically uses routing data, which identifies operations, work centers, setup time, run time, and queue or move time.

For a work center, a simplified load calculation is:

If a work center must process three jobs, each requiring 2 hours of setup and 0.5 hour per unit, and the quantities are 20, 10, and 30 units, required capacity is:

3 × 2 + 0.5 × (20 + 10 + 30) = 36 hours.

If 40 hours are available, nominal utilization is:

Thus, utilization is 36 ÷ 40 × 100% = 90%. This calculation assumes the 40 hours are genuinely available and does not automatically account for breakdowns, absenteeism, quality losses, or efficiency below standard. Practical capacity should therefore be based on realistic operating conditions.

When load exceeds capacity, managers may revise due dates, authorize overtime, subcontract work, add shifts, cross-train employees, reduce setup time, split lots, or change the MPS. A work center operating continuously near 100 percent may have poor responsiveness because small disruptions create long queues.

7. Sequencing and Scheduling

Scheduling assigns jobs to resources and time periods. Sequencing determines the order in which jobs are processed. Common dispatching rules include:

For a single machine with all jobs available at time zero, the average completion time is:

where C_j is completion time of job j and n is the number of jobs. SPT often minimizes average completion time under these assumptions, but it may not minimize lateness or maximize customer priority. Therefore, the appropriate rule depends on the performance objective.

The critical ratio is:

A ratio below 1 indicates that the job is behind schedule if no additional capacity or acceleration is provided. The ratio should be interpreted carefully when processing-time estimates are uncertain or when jobs compete for different resources.

Scheduling also involves finite versus infinite capacity. Infinite-capacity planning releases work without checking whether resources can perform it. Finite-capacity scheduling explicitly respects resource limits but may require more computation and frequent rescheduling. In practice, visual scheduling boards, advanced planning systems, and human expertise are often combined.

8. ERP Systems and Operational Integration

ERP systems integrate functional data through a common database and coordinated processes. A typical order may update customer demand, inventory availability, MPS requirements, MRP component demand, purchasing, production orders, shipment records, invoicing, and financial accounts.

Figure: ERP connects demand, planning, capacity, materials, execution, and shared operational data.

Core ERP master data includes item identifiers, units of measure, BOMs, routings, work centers, lead times, suppliers, prices, and locations. Transaction data includes sales orders, receipts, issues, completions, transfers, and invoices. A single database can reduce duplicate entry, but integration creates dependence: an inaccurate inventory transaction may affect purchasing, production, customer promises, and financial reporting simultaneously.

ERP implementation requires process design, data cleansing, user training, role-based access, testing, and change management. Organizations should avoid customizing the system merely to preserve inefficient practices. At the same time, forcing unsuitable standard processes onto a distinctive business can damage competitiveness. Cloud ERP reduces infrastructure burden but introduces concerns about cybersecurity, vendor dependence, data residency, availability, and subscription costs.

Artificial intelligence can support demand sensing, anomaly detection, predictive maintenance, supplier-risk analysis, and schedule recommendations. However, AI outputs require trustworthy data, explainable decision criteria, human oversight, and controls against discriminatory or commercially harmful outcomes. An algorithm that prioritizes profitable orders without considering contractual commitments may create legal and reputational risk.

Illustrative Case: GreenBrew Equipment

Background

GreenBrew Equipment, a fictional entrepreneurial manufacturer, produces compact commercial coffee machines. Demand has grown rapidly, but customers report late deliveries and occasional missing accessories.

Problem

The company plans finished machines using a spreadsheet, purchases components by email, and records inventory at the end of each week. The spreadsheet contains an outdated BOM: each machine is shown as requiring one filter holder, although a recent design revision requires two. The assembly work center also has a nominal weekly capacity of 240 hours but routinely loses 15 percent to changeovers and minor stoppages.

Analysis

The MPS promises 80 machines per week. Each machine requires 2 hours of assembly, so the theoretical load is 80 × 2 = 160 hours. At 85 percent effective availability, practical capacity is 240 × 0.85 = 204 hours, so assembly appears feasible. However, the BOM error creates a shortage of 80 filter holders per week. In addition, purchasing sees demand only after the weekly inventory count, extending the effective response time.

Approach and Solution

GreenBrew first establishes an approved multilevel BOM with revision dates and assigns ownership to engineering. It then introduces an MPS reviewed weekly, MRP using actual on-hand balances and supplier lead times, and CRP using practical rather than theoretical capacity. ERP transactions are created for receiving, issuing, completing, and shipping. A supplier portal is added for confirmed delivery dates. The company also applies a small safety stock to critical, long-lead components and uses a finite schedule for the bottleneck assembly cell.

Outcome

After implementation, the firm reduces component shortages, improves schedule adherence, and gains visibility into available-to-promise quantities. The ERP system does not eliminate all late deliveries; demand remains uncertain and one supplier remains unreliable. Managers therefore retain weekly exception reviews and a contingency supplier.

Learning Points

The case demonstrates that integration cannot compensate for poor master data. A corrected BOM, disciplined transactions, realistic capacity assumptions, and cross-functional governance are prerequisites for useful ERP outputs. It also shows that planning is a feedback system: execution results must update future plans.

Challenges, Governance, and Best Practices

Important limitations include forecast error, uncertain lead times, yield loss, engineering changes, machine failures, labor absence, inaccurate inventory, and conflicting departmental objectives. Planners should use scenario analysis rather than treating a single forecast as fact.

Best practices include:

• Keep BOMs, routings, lead times, and inventory records accurate.
• Separate forecast demand from firm customer orders and define commitment rules.
• Use time fences to control unnecessary MPS changes.
• Validate MRP results through CRP and supplier-capacity checks.
• Measure schedule adherence, inventory accuracy, stockouts, order lateness, capacity utilization, and expedite frequency.
• Use exception management so planners focus on material shortages, overloads, and major deviations.
• Establish authorization, audit trails, segregation of duties, and cybersecurity controls in ERP.
• Include operators, buyers, sales staff, engineers, finance personnel, and customers in process design where appropriate.
• Review AI-supported recommendations for bias, explainability, privacy, and accountability.

Operational data also raises ethical issues. Employee-performance data should be collected proportionately and used transparently. Supplier evaluation should not rely on opaque scores that unfairly penalize small firms. Customer and supplier information must be protected from unauthorized access. Compliance with applicable privacy, labor, product-safety, financial-control, and records-retention requirements is part of responsible operations management.

Chapter Summary

Operations planning forms a hierarchy from aggregate decisions to detailed execution. Aggregate planning balances demand and resources for product families using workforce, inventory, overtime, subcontracting, and backorder choices. The MPS translates that plan into time-phased end-item commitments. BOMs describe product structure, while MRP uses the MPS, BOM, inventory records, lead times, and lot-sizing rules to calculate component requirements and order releases. CRP tests whether planned work fits available work-center capacity. Sequencing and scheduling determine job order and timing, but no single dispatching rule is best for every objective.

ERP integrates these activities through shared master and transaction data. Its value depends on accurate records, disciplined processes, realistic assumptions, security, training, and governance. Modern analytics and AI can improve forecasting and exception management, but they require human oversight. Effective entrepreneurs treat planning as a continuous feedback process linking customer demand, operational capability, suppliers, financial consequences, and responsible decision-making.

Key Terms

Aggregate planning: Medium-term planning of total output, workforce, inventory, and related resources.

Available-to-promise (ATP): Quantity that can be committed to new customer orders after protecting existing commitments.

Bill of materials (BOM): Structured list of components and quantities required for a parent item.

Capacity requirements planning (CRP): Process of comparing planned workload with available work-center capacity.

Chase strategy: Aggregate plan that varies production or workforce to follow demand.

Critical ratio: Ratio of time remaining until due date to remaining processing time.

Dependent demand: Demand derived from the need for another item.

Dispatching rule: Principle used to select the next job for processing.

Enterprise resource planning (ERP): Integrated system connecting organizational processes and data.

Finite-capacity scheduling: Scheduling that explicitly respects resource limits.

Master production schedule (MPS): Time-phased plan for producing specific finished items.

Material requirements planning (MRP): Time-phased calculation of dependent-material requirements and planned orders.

Nervousness: Operational disruption caused by frequent changes to planned orders or schedules.

Projected available balance (PAB): Expected inventory position after considering demand and scheduled production.

Routing: Sequence of operations, work centers, and times required to make an item.

Safety stock: Inventory held to protect against uncertainty in demand or supply.

Sequencing: Determining the order in which jobs are processed.

Time fence: Boundary restricting changes to a production schedule within a defined period.

Utilization: Required capacity expressed as a proportion or percentage of available capacity.

Review Questions

5 Short Answer Questions

1. What is the purpose of aggregate planning?
2. How does an MPS differ from an aggregate plan?
3. What information is required for MRP?
4. Why is BOM accuracy important?
5. Define finite-capacity scheduling.

5 Long Answer Questions

1. Compare level, chase, and mixed aggregate-planning strategies, including their operational risks.
2. Explain the sequence of calculations used in an MRP system.
3. Discuss how CRP can cause a planner to revise an MPS.
4. Compare FCFS, SPT, and EDD sequencing rules and identify circumstances in which each may be appropriate.
5. Explain the benefits and risks of integrating operations through ERP.

3 Analytical / Application Questions

1. A company must produce 120 units in week 5. Each unit requires three components. There are 100 components on hand, no scheduled receipts, and a two-week lead time. Using lot-for-lot planning and no safety stock, calculate the net requirement and planned order-release week.
2. A work center has 45 available hours. Three jobs require setup times of 1, 2, and 1 hours and run times of 0.4, 0.6, and 0.5 hours per unit. Their quantities are 20, 15, and 30. Calculate total required capacity and utilization, then recommend one response if capacity is insufficient.
3. Design an ERP implementation plan for a small manufacturer whose inventory records are unreliable. Identify master data, process controls, user groups, implementation risks, and performance measures.

Multiple Choice Questions with Answers

Question 1

Which planning level determines the total production and workforce requirements for product families over a medium-term horizon?

A. Aggregate planning

B. Detailed dispatching

C. Shop-floor inspection

D. Invoice processing

Correct Answer: A. Aggregate planning

Question 2

An MPS requires 50 finished units, each using two units of component A. If 20 units of A are available and no safety stock is required, what is the net requirement?

A. 20 units

B. 50 units

C. 80 units

D. 100 units

Correct Answer: C. 80 units

Question 3

What is the primary purpose of a bill of materials?

A. To rank suppliers by price

B. To list components and quantities required for a parent item

C. To calculate employee wages

D. To record customer credit limits

Correct Answer: B. To list components and quantities required for a parent item

Question 4

A work center requires 36 hours and has 40 available hours. Its utilization is:

A. 4%

B. 40%

C. 90%

D. 111%

Correct Answer: C. 90%

Question 5

Which sequencing rule generally tends to reduce average flow time on a single machine when all jobs are available simultaneously?

A. Shortest processing time

B. Longest processing time

C. First come, first served

D. Random selection

Correct Answer: A. Shortest processing time

Question 6

What does CRP primarily compare?

A. Sales revenue with profit

B. Planned workload with available work-center capacity

C. Forecast demand with advertising expenditure

D. Supplier prices with customer prices

Correct Answer: B. Planned workload with available work-center capacity

Question 7

A component has a one-week lead time and a planned receipt in week 4. In which week should its planned order normally be released?

A. Week 1

B. Week 2

C. Week 3

D. Week 4

Correct Answer: C. Week 3

Question 8

Which statement best describes ERP?

A. A system used only for payroll

B. An integrated system connecting processes and shared organizational data

C. A forecasting method that eliminates uncertainty

D. A scheduling rule used only on one machine

Correct Answer: B. An integrated system connecting processes and shared organizational data

Question 9

What is a major consequence of inaccurate ERP master data?

A. All forecasts become perfectly accurate

B. Errors can propagate across purchasing, production, customer commitments, and finance

C. Capacity constraints disappear

D. Supplier lead times become legally fixed

Correct Answer: B. Errors can propagate across purchasing, production, customer commitments, and finance

Question 10

A critical ratio below 1 generally indicates that a job:

A. Has no due date

B. Is ahead of schedule

C. Is behind schedule if no acceleration occurs

D. Requires no processing time

Correct Answer: C. Is behind schedule if no acceleration occurs