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    Supply chain analytics

    Gilvan C. Souza

    Kelley School of Business, Indiana University, Bloomington, IN 47405, U.S.A.

    1. Why analytics in supply chainmanagement?

    The

    supply

    chain

    for

    a

    product is

    the

    network offirms and facilities involved in the transformationprocess from raw materials to a product and inthe distribution of that product to customers. Ina supply chain, there are physical, financial, and

    informational flows among different firms. Supplychain analytics focuses on the use of informationandanalytical

    tools

    to

    make

    better

    decisions regard-ing material flows in the supply chain. Putdifferently, supply chain analytics focuses on

    analytical

    approaches

    to

    make

    decisions

    that

    bettermatch supply and demand.Well-planned and implemented decisions con-

    tribute directly to the bottom line by loweringsourcing, transportation, storage, stockout, anddisposal costs. As a result, analytics has historicallyplayed a significant role in supply chain manage-ment, starting with military operations during and

    after World War IIparticularly

    with the

    develop-ment of the simplex method for solving linear pro-gramming by George Dantzig in the 1940s. Supplychain analytics became more ingrained in decisionmaking with the advent of enterprise resource plan-ning (ERP) systems in the 1990s and more recentlywith big data applications, particularly in descrip-tive and

    predictive

    analytics,

    as

    I describe

    withsome examples in this article.

    Business

    Horizons

    (2014)

    57, 595605

    Available online at www.sciencedirect.com

    ScienceDirectwww.elsevier.com/locate/bushor

    KEYWORDS

    Supply chainmanagement;Analytics;Optimization;Forecasting

    Abstract In this article, I describe the application of advanced analytics techniquesto supply chain management. The applications are categorized in terms of descrip-tive,

    predictive,

    and

    prescriptive

    analytics

    and

    along

    the

    supply

    chain

    operationsreference (SCOR) model domains plan, source, make, deliver, and return. Descriptiveanalytics applications center on the use of data from global positioning systems(GPSs), radio frequency identification (RFID) chips, and data-visualization tools toprovide

    managers

    with

    real-time

    information

    regarding

    location

    and

    quantities

    ofgoods in the supply chain. Predictive analytics centers on demand forecasting atstrategic, tactical, and operational levels, all of which drive the planning process insupply chains in terms of network design, capacity planning, production planning, andinventory

    management.

    Finally,

    prescriptive

    analytics

    focuses

    on

    the

    use

    of

    mathe-matical optimization and simulation techniques to provide decision-support toolsbuilt upon descriptive and predictive analytics models.

    #

    2014

    Kelley

    School

    of

    Business,

    Indiana

    University.

    Published

    by

    Elsevier

    Inc.

    Allrights reserved.

    E-mail

    address:

    [email protected]

    0007-6813/$

    see

    front

    matter # 2014 Kelley School of Business, Indiana University. Published by Elsevier Inc. All rights reserved.

    http://dx.doi.org/10.1016/j.bushor.2014.06.004

    http://dx.doi.org/10.1016/j.bushor.2014.06.004http://dx.doi.org/10.1016/j.bushor.2014.06.004http://dx.doi.org/10.1016/j.bushor.2014.06.004http://dx.doi.org/10.1016/j.bushor.2014.06.004http://dx.doi.org/10.1016/j.bushor.2014.06.004http://dx.doi.org/10.1016/j.bushor.2014.06.004http://dx.doi.org/10.1016/j.bushor.2014.06.004http://dx.doi.org/10.1016/j.bushor.2014.06.004http://www.sciencedirect.com/science/journal/00076813mailto:[email protected]://dx.doi.org/10.1016/j.bushor.2014.06.004http://dx.doi.org/10.1016/j.bushor.2014.06.004mailto:[email protected]://www.sciencedirect.com/science/journal/00076813http://dx.doi.org/10.1016/j.bushor.2014.06.004http://crossmark.crossref.org/dialog/?doi=10.1016/j.bushor.2014.06.004&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1016/j.bushor.2014.06.004&domain=pdf
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    The Supply Chain Operations Reference (SCOR)model developed by the Supply Chain Council(www.supply-chain.org) provides a good frameworkfor classifying the analytics applications in supplychain management.

    The

    SCOR

    model

    outlines

    fourdomains of supply chain activities: source, make,deliver, and return. A fifth domain of the SCOR

    modelplanis behind

    all

    four

    activity

    domains.Furthermore, a key input of the supply chain plan-ning process is demand forecasting at all timeframes: long, mid, and short term with planninghorizons of years, months, and days, respectively.Table 1 illustrates different decisions in each of thefour SCOR domains that can be aided by analytics.These decisions are further classified into strategic,tactical, and operational according to their timeframe.Analytics techniques can be categorized into

    three types: descriptive, predictive, and prescrip-tive. Descriptive

    analytics

    derives

    information

    from

    significant amounts of data and answers the ques-tion of what is happening. Real-time informationabout the location and quantities of goods in thesupply chain

    provides

    managers

    with

    tools

    to

    makeadjustments to delivery schedules, place replenish-mentorders, place emergency orders, change trans-portation

    modes,

    and

    so

    forth.

    Traditional

    datasources include global positioning system (GPS) dataon the location of trucks and ships that containinventories, radio frequency identification (RFID)data originating

    from

    passive

    tags

    embedded

    in

    pallets (even at the product level), and transactionsinvolving barcodes. Information is derived from thevast amounts of data collected from these sourcesthrough data visualization, often with the help ofgeospatial mapping

    systems.

    RFID

    is

    a

    significantimprovement over barcodes because it does notrequire direct line of sight. Accurate inventory re-

    cords are

    critical

    in

    supply

    chains

    as

    they

    triggerregular replenishment orders and emergency orderswhen inventory levels are too low. Although RFIDtechnology helps in significantly reducing the fre-quency of manual inventory reviews, such reviewsare still needed because of data inaccuracy due to,for example, inventory deterioration or damage oreven tag-reading errors.Predictive analytics in supply chains derives de-

    mand forecasts

    from

    past

    data

    and

    answers

    thequestion of what will be happening.Prescriptive analytics derives decision recom-

    mendations

    based

    on

    descriptive

    and

    predictive

    analytics models and mathematical optimizationmodels. It answers the question of what should behappening. Arguably, the bulk of academic re-search, software,

    and

    practitioner

    activity

    in

    supplychain analytics focuses on prescriptive analytics.In Table 2, I provide a summary of analytics

    techniquesdescriptive,

    predictive,

    and

    prescrip-tiveused in supply chains in terms of the four SCORdomains of source, make, deliver, and return. Ielaborate on Table 1 and Table 2 in the nextsections.

    Table

    1.

    SCOR

    model

    and

    examples

    of

    decisions

    at

    the

    three

    levels

    SCOR

    Domain

    Source

    Make

    Deliver

    Return

    Activities Order and receivematerials andproducts

    Schedule andmanufacture, repair,remanufacture,

    orrecycle

    materialsand products

    Receive, schedule,pick, pack, andship

    orders

    Request, approve, anddetermine disposal ofproducts

    and

    assets

    Strategic

    (time frame:years)

    Strategicsourcing

    Supply chainmapping

    Location of plantsProduct line mixat plants

    Location ofdistribution centers

    Fleet planning

    Location of returncenters

    Tactical(time frame:months)

    Tactical sourcingSupply chaincontracts

    Product linerationalization

    Sales andoperations planning

    Transportation anddistribution planning

    Inventory policiesat locations

    Reverse distributionplan

    Operational

    (time

    frame:days)

    Materialsrequirementplanningand inventoryreplenishmentorders

    Workforce schedulingManufacturing,

    ordertracking, and scheduling

    Vehicle routing(for

    deliveries)

    Vehicle routing (forreturns

    collection)

    Plan Demand forecasting (long term, mid term, and short term)

    596 G.C. Souza

    http://www.supply-chain.org/http://www.supply-chain.org/
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    2. Plan: Demand forecasting usingpredictive analytics

    Demand forecasting is a critical input to supplychain planning.

    Different

    time

    frames

    for

    demand

    forecasting require different analytics techniques.Long-term demand forecasting is used at the stra-tegic level and may use macro-economic data, de-mographic trends, technological trends, andcompetitive intelligence. For example, demand fac-tors for commercial aircraft at Boeing include ener-gy prices, discretionary spending, populationgrowth, and inflation, whereas demand factors formilitary aircraft include geo-political changes, con-gressional spending, budgetary constraints, andgovernment regulations (Safavi, 2005). Causal fore-casting methodscalled

    such

    because

    they

    analyze

    the underlying

    factors that

    drive

    demand

    for aproductare used at this level. Analytics causalforecasting

    methods

    include

    linear, non-linear,and logistic regression.To illustrate demand forecasting for tactical and

    operational supply chain decisions, consider theproduction

    planning

    process

    for

    an

    original

    equip-ment manufacturer (OEM) such as Whirlpool. At theproduct family level (e.g., refrigerators), the salesand operations

    planning

    (S&OP)

    process

    uses

    aggre-gate demand forecasts in monthly time buckets toestablish aggregate production rates, aggregatelevels of inventories, and workforce levels. Theaggregate plan is revised on a rolling basis as newdata is available. The S&OP plan, as well as morerefined demand forecasts at the stock-keeping unit(SKU) level, is used to derive the master productionschedule (MPS), which details weekly productionquantities at the SKU level for a typical planninghorizon of 812 weeks. The MPS and the bill ofmaterials are

    then

    used

    to

    plan

    production

    andsourcing at the part level through a materials re-quirement planning (MRP) system that is embeddedinmost ERP software.Time-based demands for parts

    are derived from time-based demands for theSKUs that use those parts, so parts have dependentdemand. In contrast, SKUs have independentdemand. Demand forecasts for items subject to inde-pendent

    demand require

    predictive

    analytics techni-

    ques,whereasforecasts fordependent demanditemsare obtained directly from the MRP system. Demandforecasts for independent demanditemsarealsousedtoplan for inventory safety stocks at other locations,such as distribution centers and retailers.Demand forecasting for independent demand

    items isusuallyperformedusingtime-seriesmethods,forwhich the only predictor of demand is time. Time-series methods include moving average, exponentialsmoothing, andautoregressive models. For example,Wintersexponential smoothingmethodincorporatesboth trend

    and

    seasonality

    and can

    be

    used

    for

    both

    short-term and

    mid-term forecasting.

    In

    an

    autore-gressive model, demand forecast in one period is aweighted sum of

    realized demands

    in

    the previousperiods.Mid-term forecasting can also benefit from

    causal forecasting methods, especially in non-manufacturing industries

    or

    the

    manufacturing

    ofnon-discrete items. For example, in order to fore-cast monthly demand for truckload (TL) freightservices, Fite,

    Taylor,

    Usher,

    English,

    and

    Roberts(2002) considered 107 economic indexes as poten-tial predictors, including the purchasing managersindex, the Dow Jones stock index, the consumergoods production index, automotive dealer sales,U.S. exports, the producer commodities price indexfor construction materials and equipment, interestrates, and gasoline production. They used stepwiseregression to identify the most relevant indexes andfound parsimonious models for predicting TL de-mand for specific industries and regions. Their mod-el only

    predicts

    industry-wide

    demand

    for

    TLservices (nationally or by region); the connectionto demand forecasts at the firm level was madeusing historical market shares.

    Table

    2.

    Analytic

    techniques

    used

    in

    supply

    chain

    management

    Analytics

    Techniques

    Source Make Deliver Return

    Descriptive Supply

    chain

    mapping Supply

    chain

    visualization

    Predictive Time series methods (e.g., moving average, exponential smoothing, autoregressive models) Linear, non-linear, and logistic regression Data-mining techniques (e.g., cluster analysis, market basket analysis)

    Prescriptive Analytic hierarchy process Game theory (e.g., auction design,contract design)

    Mixed-integer linearprogramming (MILP)

    Non-linear programming

    Network flowalgorithms

    MILP Stochasticdynamicprogramming

    Supply chain analytics 597

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    Data mining has also been used for demand fore-casting in conjunction with traditional forecastingtechniques (Rey, Kordon, & Wells, 2012). Usually,the data-mining step precedes the use of causalforecasting techniques

    by

    finding

    appropriate

    de-mand drivers (i.e., independent variables) for aproduct that can be used in regression analysis.

    For example,

    Dow

    Chemical

    uses

    a

    combination

    ofdata mining and regression techniques to forecastdemand at the strategic and tactical levels (e.g.,identifying demand trends), which is useful for itspricingstrategy and for configuring and designing itssupply chain to respond to these trends (Rey&Wells,2013). Data-mining methods usually involve cluster-ing techniques. So, if a retailer finds out, for exam-ple, that demand for cereal is strongly related tomilk sales,

    then

    the

    retailer

    may

    build

    a

    causalforecasting model that predicts cereal sales withmilk sales as one of the predicting variables. Marketbasket analysis

    is

    a

    specific

    data-mining

    technique

    that provides an analysis of purchasing patterns atthe individual transaction level, so a retailer cananalyze the frequency with which two product cat-egories

    (e.g.,

    DVDs

    and

    baby

    products)

    are

    pur-chased together. Lift for a combination of items isequal to the actual number of times the combina-tion occurs

    in

    a

    given

    number

    of

    transactions

    dividedby the predicted number of times the combinationoccurs if items in the combination were indepen-dent. Lift values above 1 indicate that items tend tobe purchased

    together.

    This

    kind

    of

    analysis

    can

    beuseful when building causal regression models for

    demand

    forecasting. It

    can

    also

    aid

    in

    promotionactivitiesbecause the retailer can predict how muchsales of Product 1 would increase if there is apromotion for Product 2 if the two products areoften purchased together.

    3. Source

    3.1. Source: Strategic decisions

    Strategic sourcing is the process of evaluating andselecting key suppliers. There is limited use ofanalytics for

    strategic

    sourcing

    in

    practice

    eventhough academics prescribe the use of sophisticatedmulti-criteria decision-making techniques such asanalytic hierarchic process (AHP). AHP decomposesa complex problem (e.g., selecting a supplier amonga diverse set) into more easily comprehended sub-problems that can be analyzed separately. In thesupplier-selection problem, these sub-problemsmight include distinct evaluations of factors likecost, quality, delivery speed, delivery reliability,volume flexibility, product mix flexibility, and sus-tainability. These evaluations are then weighed.

    Firms are very familiar with their first-tier sup-pliers (i.e., those that directly supply them) andperhaps their second-tier suppliers (i.e., those thatsupply first-tier suppliers), but some of their lower-tier suppliers

    may

    be

    unknown.

    A

    recent

    example

    isthe November 2012 fire at the Bangladesh factorythat killed more than 100 workers. An audit of the

    factory by

    Walmart

    in

    2011

    ruled

    it

    out

    as

    a

    supplier.However, one of Walmarts suppliers continued tosubcontract work to that factory (Tsikoudakis,2013). The threat of disruptions like natural disas-ters, social and political unrest, and major strikesmakes it imperative for firms to map their supplychains. For example, Cisco (2013) uses supply chainmapping and enterprise social networking to iden-tify its vulnerabilities to supply chain disruptions aswell as

    to

    collaborate

    with

    its

    suppliers

    and

    part-ners. The open source tool sourcemap.com, devel-oped at the Massachusetts Institute of Technology,allows one

    to

    visualize

    and

    map

    a

    supply

    chain;

    the

    tool can also be used for purposes such as carbonfootprint estimation. An example is shown inFigure 1.

    3.2. Source: Tactical decisions

    In

    contrast

    to

    strategic sourcing,

    tactical

    sourcingrefers to the process of achieving specificobjectivessuch as determining costs for parts,materials, or servicesthrough structured procure-ment mechanisms

    like

    auctions.

    The

    central

    prob-lem in procurement auctions centers on mechanism

    design:

    How

    should

    one

    structure

    the

    rules

    of

    anauction so that bidders (i.e., suppliers) behave in amanner that results in minimal procurement cost(and desired performance) for the buyer? Auctionscan be open (i.e., bidders can view and respond tobids) or

    sealed

    and

    one

    shot

    or

    dynamic

    (whichoccurover several rounds of bidding). Government auc-tions tend to be one-shot, sealed auctions, whereasopen, dynamic auctions are common in industrialprocurement (Beil, 2010). Buyers must consider thetotal procurement cost as bidders usually bid oncontract payment terms only (e.g., unit cost). Ad-ditional logistics

    costs,

    if

    paid

    by

    the

    buyer,

    must

    betaken into account in the bid price. The prescriptiveanalytics used here is centered on game theory,which is used to determine auction rules. Procure-ment auctions are widely used in practice.A commonly used payment contract in sourcing is

    wholesale price, via which the buyer (i.e., retailer)pays the seller (i.e., manufacturer) a fixed price perunit. Under this contract, retailers are exposed todemand risk: they bear the entire costs of over-stocking and therefore have an incentive to stockless than what is optimal for the supply chain as a

    598 G.C. Souza

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    whole. Recognizing this, academics have used acombination of game theory and statistics to pre-scribe more sophisticated contracts that will im-prove product availability in retailers. For example,in a buy-back contract, retailers can return unsoldunits to the manufacturer and receive a partialrefund. Although

    such

    contracts

    can

    improve

    supplychain performance, the wholesale price contract isstill widely used, perhaps due to its simplicity.

    4. Make

    4.1. Make: Strategic decisions

    Network design determines the optimal location andcapacity of plants, distribution centers (DCs), andretailers. The simplest form of the network design

    problem can be illustrated when deciding where tobuild DCs that serve as intermediary stockingand shipping points between existing plants andretailers. This problem is formulated as a mixed-integer linear program (MILP). Data requirementsinclude yearly aggregate demands for the productfamily at

    each

    retailer,

    plant

    capacities,

    unit

    ship-ping costs between each pair of locations, and theannual fixed cost of operating a DC at each potentiallocation. Decision variables include the quantity toship between locations and binary variables thatindicate if each DC should be open or closed. Theobjective function minimizes total shipping andfixed DC costs. Constraints ensure that demand ismet at all locations, that companies only ship prod-ucts from a DC if it is open, and that all plantcapacities are respected. The solution providesthe location (i.e., where to open the DCs) as well

    Figure 1. Example of supply chain mapping using sourcemap.com

    Source:

    free.sourcemap.com/view/6585/

    Supply chain analytics 599

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    as the allocation of plants to the DCs, the allocationof DCs to retailers, and the capacity of each DC.Variations of this simple MILP formulation include

    multipleproducts, transportation capacitiesbetweenlocations,

    multiple

    transportation modes

    betweenlocations, a multi-year planning horizon, multipleechelons (i.e., tiers in the supply chain), demand

    uncertainty,

    supply

    uncertainty,

    and reverse

    flows(e.g., the collection of used products for recyclingand remanufacturing). When the problem incorpo-ratesmultipleproducts, theanalysis alsoprovides theproduct mix at each plant. When many of the varia-tions above are incorporated andthe problem is large(e.g., thousands of retailers and potential DC andplant locations), the problem may become too diffi-cult to solve to optimality using off-the-shelf optimi-zation software.

    Therefore,

    many researchers

    haveproposed well-performing heuristics, such as geneticalgorithms, that ensure goodand sometimesoptimalsolutions. Genetic

    algorithms use

    a

    divide

    and conquer (the feasible region) approach to findinga good solution to the MILP as opposed to optimalbranch and bound algorithms, which are combinato-rial in nature.Some of the data necessary to perform such

    analysis requires a preliminary level of analysis soit can

    be

    extracted,

    cleaned,

    and

    aggregated

    fromERP systems. Network design, however, is only per-formed infrequently for each firm, including duringmergers and acquisitions. As a result, it is not part ofstandard ERP

    software.

    Specialized

    software

    makesit easy to input this data, specify the constraints,

    perform

    the

    optimization,

    and

    visualize

    the

    results,especially for large problems.

    4.2. Make: Tactical decisions

    We have

    previously

    described

    the

    S&OP

    process,which is used for planning aggregate workforceand inventory levels on a medium planning horizonbased on demand forecasts, underlying costs, andactual sales. Academics have proposed MILP modelsfor this process. For each month in the planninghorizon, decision variables include the amount toproduce for

    each

    product

    family

    using

    regular

    time,overtime, and subcontracting and the number ofworkers to be hired and laid off. The objectivefunction minimizes total cost, which comprises totalproduction cost (i.e., regular time, overtime, andsubcontracting), total inventory cost, total wages,total hiring cost, and total layoff cost. Constraintsmay come from, among others, inventory and work-force balancing, regular production capacity,and overtime production. Many practitioners userules-based heuristics. For example, one heuristicis a level production strategy, via which the firm

    meets fluctuating demand byproducing at a constantrateandholding inventory tomeet thepeakdemand.Alternatively, the firm can use a chase strategy,adjusting workforce levels monthly tomeetfluctuat-ing demand.

    Firms

    frequently

    use

    a

    hybrid

    strategybetween chase and level.Productproliferationandmasscustomizationhave

    been widely

    documented

    (e.g.,

    Rungtusanatham

    &Salvador, 2008). For product proliferation and masscustomization, the plant must adapt from a massproduction environmentdesigned for economiesof scale, with fewer products produced in dedicatedlines and setup costs spread over long productionrunsto a flexible production environment. Thisadaptation is made possible with the aid of flexiblemanufacturing technology or changes in the productand process

    design that

    support

    a

    postponementstrategy (Lee, 1996). In a postponement strategy,the step in the manufacturing process in which prod-uct differentiation

    occursfrom

    gray boxes

    to

    SKUsis located closer to thecustomer, whichallowsthe firm to carry inventory of gray boxes instead ofSKUs, and thus lessens differentiation time. Post-ponement mitigates the

    negative

    impacts

    of

    in-creased product proliferation, such as increasedforecasting uncertainty at the SKU level; increasedinventory costs;

    and

    complexity costs,

    such

    as

    re-search and development, testing, tooling, returns,andobsolescence.Postponement requires changes inproduct and process design, and itmay not be feasi-ble for

    products

    like

    automobiles,

    for

    which

    strictquality guidelines in final assembly preclude signifi-

    cant

    customization

    at

    dealers.

    As

    an

    alternative,firmsmay increase supply chainperformance throughproduct rationalization using analytics, as shown inTable 3.

    4.3. Make: Operational decisions

    Manufacturing scheduling is the last step in theplanning process after MRP plans are released. AnMRP plan specifies quantities and due dates for allparts. Scheduling then sequences the jobs (i.e.,parts) by the different resources necessary formanufacturing

    the

    part

    in

    order

    to

    meet

    the

    duedates. In general, there are n jobs to be scheduled inm different resources, and the processing time, duedate, and weight (i.e., priority) of each job in eachresource are known. This problem takes differentforms depending on the decision makers objective,the number of resources, and how the jobs areprocessed with the resources. An objective functionminimizes the maximum completion time, or themaximum lateness, across all jobs. There can beprecedence relationships, setup times, or evensequence-dependent setup times (i.e., when the

    600 G.C. Souza

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    setup time for a job at a resource depends on theprevious job there, such as in processing industrieslike the chemical industry). Scheduling problemscan be formulated as MILPs, and the combinatorial

    nature of these problems makes them very hard tosolve to

    optimality

    for

    large

    problems.

    As

    a

    result,significant effort has been devoted to finding goodsolutions through heuristics because other compli-cations arise in practice, such as adding new jobs totheexisting pool of processing jobs as well as chang-ing priorities

    and

    preferences.

    In

    terms

    of

    software,some ERP systems have scheduling modules (e.g.,the Applied Planning and Optimization module inSAP) that use genetic algorithms to provide goodsolutions to MILPs found in determinist scheduling.Thesealgorithms can provide good solutions to fairly

    large problems,

    such

    as

    1

    million

    jobs

    over

    1,000resources

    (Pinedo,

    2008).

    There

    are

    a

    few

    compa-nies such as Taylor (www.taylor.com) that specializein providing scheduling softwarewith many function-alities not

    present in

    ERP systems.

    Although

    thediscussion above has centered on manufacturingscheduling, some of the same algorithms can be usedin other scheduling problems like assigning gates atan airport

    or

    trucks

    at

    a

    cross-docking

    location.Workforce scheduling can be challenging for ser-

    vice industries, such as call centers, hospitals, andairlines, in which there is seasonal demand, not onlyfor time of the year (common inmanufacturing), butalso for day of the week and hour of the day. Acommon way of modeling these problems isby defining

    tours.

    A

    tour

    is

    a

    combination

    of

    timeblockswithin a day and within days of the week thatadd up to the necessary work hours per employee.An example of a tour would be Monday, 8 a.m.1p.m.; Tuesday, 1 p.m.6 p.m.; Thursday, 8 a.m.6p.m.; and Friday, 8 a.m.6 p.m. Tours should befeasible; for example, it is not very convenient formost people

    to

    work

    from

    8

    a.m.10

    a.m.

    andthen from 3 p.m.5:00 p.m. on the same day.

    The decision maker needs demand forecasts foreach time block (e.g., 12 p.m.1 p.m. on Monday),which can be obtained through predictive forecast-ing models. This problem can be formulated as an

    MILP in which decision variables include the numberof employees

    assigned

    to

    each

    tour

    and

    the

    numberof employees necessary to meet demands withineach time block. The objective function minimizestotal labor costs. Complications, such as workerspreferences, multiple locations, task assignments,and so

    forth,

    increase

    the

    size

    of

    the

    MILP

    model

    tosuch an extent that heuristics are almost certainlyneeded. Some ERP vendors have workforce sched-ulingmodules for specific applications like retail andhospitality. There are also vendors for industry-spe-cific software, such as call centers and health care

    providers.

    Many

    airlines,

    which

    are

    heavy

    analyticsusers, have

    developed

    their

    own

    scheduling

    algo-rithms.

    5. Deliver and return

    5.1. Deliver and return: Strategicdecisions

    In Section 4, I presented the network design problemof planning the location of DCs and return centers.Another strategic decision here is fleet planning,which can be described as the dynamic acquisitionand divestiture of delivery vehicles to meet thedemand for

    deliveries

    or

    returns

    collection.

    Thisproblem is formulated as an MILP, or dynamic pro-gramming, as in Table 4.

    5.2. Deliver and return: Tactical decisions

    In transportation and distribution planning, the firmdistributes

    a

    set

    of

    products

    from

    source

    nodes

    (i.e.,supply points such as factories) to sink nodes

    Table

    3.

    Product

    rationalization

    at

    Hewlett-Packard

    Hewlett-Packard (HP) has developed optimization tools for product rationalization (Ward et al., 2010). One toolrequires proposed new product line extensions to meet minimum complexity return-on-investment (ROI)thresholds.

    Complexity

    ROI

    is

    defined

    as

    the

    incremental

    margin

    minus

    variable

    complexity

    costs,

    divided

    by

    fixedcomplexity costs. Variable complexity costs are largely driven by forecasting uncertainty and resulting increasedinventory costs, whereas fixed complexity costs are driven by criteria such as research and development, tooling,and manufacturing setup costs. With another tool, HP uses a maximum flow algorithm on an existing product line to

    perform

    product

    rationalization.

    The

    tool

    acknowledges

    that

    in

    firms

    with

    configurable

    product

    lines,

    someproducts, such as power supplies, may generate little revenue on their own but are critical components for high-revenue orders and for overall order fulfillment. Order coverage is defined as the percentage of a given set of pastorders that can bemet from the rationalized product portfolio. Similarly, revenue coverage is the smallest portfolioof products that covers a given percentage of historical order revenue. This optimization tool revealed how HP canoffer only 20% of previously offered features in laptops and reach 80% revenue coverage. After implementing therecommendations, HP realized significantly reduced inventory costs and increased gross margins.

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    (i.e., demand points such as retail locations)through intermediary storage nodes (e.g., DCs).Thisproblem is solved using a multi-commodity networkflowmodel,

    which

    is

    a

    linear

    programming

    formula-tion with a special structure. In the network formu-lation, there can be multiple arcs between each pair

    of nodes. Each arc represents a shippingmodewith agiven capacity,

    such

    as

    rail,

    truckload

    (TL),

    less

    thantruckload (LTL), and air. The amount to ship in eacharc in the network for each commodity and timeperiod is

    considered.

    Constraints

    include

    capacity

    ateach arc, time period, and node, as well as flow-balancing at each node. Data requirements includeshipping costs in each arc, forecasts of supply avail-able at each source node (provided by the S&OPplan), point forecasts for demand at each sink node(from predictive analytics models), and arc capaci-ties. Economies

    of

    scale

    in

    shipping

    can

    also

    be

    incorporated.

    Problems

    of

    realistic

    size have

    thou-sands of nodes, resulting in millions of decisionvariables. However, such problems can be solvedefficiently with numerical algorithms based on thenetwork simplex

    method,

    which

    is

    embedded

    insupply chain optimization software. Despite exten-sive planning, disruptions (e.g., traffic, weather)and demand uncertainty often require plan modifi-cation, and descriptive analytics tools can be quitevaluable. For example, the Control Tower descrip-tive analytics system allows Procter & Gamble (P&G)to see

    all

    the

    transportation

    occurring

    in

    its nearsupply chain (i.e., inbound, outbound, raw materi-als, and finished product). With this technology,P&G has reduced deadhead movement (i.e., whentrucks travel empty or not optimally loaded) by 15%and thus has reduced costs (McDonald, 2011).Another important decision is determining

    supply levels

    at

    nodes in

    a

    distribution

    networkthat is, setting inventory policies. The science forsetting inventory policies (i.e., reorder point andorder-up-to level or order quantity) for a productat a single location, such as a DC, is mature, evenwhen demand is uncertain and non-stationary and

    replenishment lead times are variable. Data re-quirements include historic demand and forecastingdata, replenishment lead times, the desired servicelevel (i.e.,

    a

    desired

    fill

    rate

    or

    stock-out

    probabili-ty), holding cost, and the fixed cost of placing areplenishment order. The inventory policy parame-

    tersreorder point and order quantitycan becomputed

    using

    exact

    algorithms

    or

    approximateformulas, which are embedded in most supply chainsoftware, including in some ERP systems modules.More

    often, the supply chain

    has

    multiple stockingpoints for the same product. For example, a productcanbe stockedataDCandmultipledifferent retailersin different regions. Although one can set inventorypolicies at each location that use only local demandand replenishment lead-time information, this localoptimization approach is not optimal for the supplychain. Due

    to risk

    pooling,

    it

    may

    be

    optimal

    to

    have

    some level of

    inventory

    at

    the DC

    so that

    higher-than-normaldemand inoneretailercanbebalancedagainstlower-than-normal demand at another retailer. Thissituation calls for an integrated inventory policy forthe entire

    supply chain; the

    theory

    that prescribestheseinventorypolicies is calledmulti-echelon inven-tory theory.Thecomplication inmulti-echelon inven-torytheoryariseswhentheDCdoesnothavesufficientinventory tomeetall incomingorders fromretailersata given period. In that case, the optimal inventory-rationing policy is complex, and even more so if thereare more

    than two

    echelons.

    There

    are,

    however,several well-performing heuristics that are computa-tionally simple, such as the guaranteed service levelheuristic (Graves & Willems, 2000), which has beenimplemented in software like Optiant. An example ofsuccessful application is provided in Table 5.

    5.3. Deliver and return: Operationaldecisions

    The vehicle routing problem (VRP) optimizes thesequence of nodes to be visited in a route, forexample, for a parcel delivery truck, for a returns

    Table

    4.

    Fleet

    planning

    for

    Coca-Cola

    Enterprises

    Coca-Cola Enterprises (CCE) has started replacing some of its fleet of diesel delivery trucks with diesel-electrichybrid vehicle (HEV) trucks. How the company chooses to invest those dollars depends on volatile fuel costs, usage-based

    deterioration,

    and

    seasonal

    demand.

    Wang,

    Ferguson,

    Hu,

    and

    Souza

    (2013)

    have

    provided

    a

    prescriptiveanalytics model that takes into consideration CCEs historical maintenance costs, purchasing costs for both dieseland HEV trucks, CCE demand data, and historical diesel price data to calibrate a stochastic model that simulatesdiesel prices dynamically. Using dynamic programming, the optimal policy is obtained, at each period of a planning

    horizon

    and

    for

    each

    realization

    of

    diesel

    prices,

    that

    determines

    how

    many

    trucks

    of

    each

    type

    (diesel

    and

    HEV)CCE should acquire and/or divest. Wang et al. found that at the current outlook of diesel prices, CCE should includeboth HEV (54%) and diesel trucks (46%) in its capacity portfolio. In this regard, CCE could use HEV trucks to meet itsaverage baseline demand and then deploy diesel trucks to supplement the delivery fleet during peak demandseasons.

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    collection truck, or for both. The optimal sequencetakes into account the distances between each pairof nodes; expected traffic volume; left turns; andother constraints placed on the routes, such asdelivery and pickup time windows. Known as thetravelling salesman problem (TSP), the classical VRPproblem only

    takes

    into

    account

    the

    distances

    be-

    tween each

    pair

    of

    nodes:

    In

    what

    sequence

    shouldnodes be visited, ending at the same starting point?This problem can be formulated as an MILP. The TSPproblem is combinatorial in nature, and is hardto solve

    beyond

    a

    few

    thousand

    nodes

    (Funke

    &Gruenert, 2005). Among others, complications suchas multiple vehicles, vehicle capacities, tour-lengthrestrictions, and delivery and pickup time windowsresult in an MILP that is very difficult to solve, thusrequiring heuristic approaches. In addition to heu-ristic approaches, vehicle-routing software incorpo-rates descriptive

    analytics,

    as

    shown

    in

    Table

    6.

    6. Modulating demand to matchcapacity: Revenue management

    The SCOR model implicitly assumes that managersplan their operationssource, make, deliver, andreturnbased on demand forecasts. Therefore, theSCOR model plans capacity to match a given de-mand. Industries

    with

    perishable

    capacities,

    likeairlines, hospitality, and transportation, must takea reverse approach, so firms modulate their demand

    to match their fixed capacity through prices andother mechanisms that will be described next. Thisis known as revenue management.Revenue management started in the airline in-

    dustry after deregulation, with the problem of allo-cating seats in a flight to fare classes. Allocationpolicies are

    nested.

    For

    instance,

    suppose

    there

    are

    two fare

    classes:

    $150

    (Fare

    Class

    1)

    and

    $90

    (FareClass 2). The decision maker sets a booking limit forFare Class 2 and then determines the booking limitof Fare Class 1 based on the capacity of the flight.Data requirements

    for

    the

    computation

    of

    bookinglimits include demand forecasts for the differentclasses (as a probability distribution) at differenttimes before departure, cancellation probabilities,up-selling probabilities (i.e., the probability that acustomer will buy a higher fare if the lower fare isunavailable), and fare values. The problem is sig-nificantly more

    complex

    in

    a

    network.

    For

    example,one passenger goes from Indianapolis (IND) toNew York (JFK), whereas another passenger goesfrom IND to Rochester (ROC) via JFK. In this case,heuristic approaches, such as bid-price controls, areused. The bid price for a resource (e.g., a seat in aspecific flight IND-JFK) is the marginal cost to thenetwork of

    consuming

    one

    unit

    of

    that

    resource.When a customer demand arises (e.g., IND-ROC viaJFK), then the demands revenue is comparedagainst the sum of bid prices for all resources asso-ciated with the demand request (i.e., bid prices fora seat IND-JFK and for a seat JFK-ROC). The demand

    Table

    5.

    Multi-echelon

    inventory

    management

    at

    P&G

    Before 2000, P&G used only single-location inventory models, which optimize inventory levels locally given thatlocations own replenishment lead time. However, starting in 20052006, P&G started implementing multi-echeloninventory

    models

    based

    on

    the

    guaranteed

    service

    level

    heuristic

    in

    its

    more

    complex

    supply

    networks.

    At

    aparticular stage in the supply chain, inventory is set to meet a desired service level based on a guaranteed deliverytime to the customer (S), its own replenishment lead time when ordering from a preceding stage (SI), and itsprocessing time (T). Essentially, the method sets safety stock levels as if it was a single location with a

    replenishment

    lead

    time

    of

    SI

    +

    T

    -

    S.

    Note

    that

    SI

    for

    a

    stage

    is

    equal

    to

    S

    for

    a

    preceding

    stage.

    Through

    dynamicprogramming, the method finds the optimal S for each stage to minimize holding costs across the supply chain. Themulti-echelon supply chain approach to inventory management was implemented at 30% of P&Gs locations usingOptiant software and consequently saved the company $1.5 billion in inventory costs in 2009 compared to thesingle-location models previously in place (Farasyn et al., 2011).

    Table 6. Vehicle routing at Waste Management, Inc.

    Waste Management, Inc. (WM) is a leading provider of solid waste collection and disposal services. It has a fleet ofmore

    than

    26,000

    vehicles

    running

    nearly

    20,000

    routes.

    In

    2003,

    the

    company

    implemented

    the

    WasteRoutevehicle-routing software, which included GIS capabilities and navigational capabilities, and integrated it with arelational database containing customer information. An origin-destination matrix was then developed thatconsidered constraints such as time and distance traveled between any two points, speed limits, and one-waystreets. By implementing the combined prescriptive and descriptive analytics software, the firm saved $44 millionin 2004.

    Source:

    www.informs.org

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    is accepted if the revenue is higher than the sum ofbid prices. Bid prices can be approximated throughlinear

    programming.

    In capacity allocation, fare prices are given asthey are determined by market forces. Another wayto manage uncertain demand for fixed capacitybeit flight

    seats,

    hotel

    rooms,

    rental

    cars,

    or

    inventoryin a retail environmentis through pricing. As ar-gued by Talluri and Van Ryzin (2004, p. 175), thedistinction

    between

    quantity

    and

    price

    controls

    isnot always sharp (for instance, closing the availabil-ity of a discount class can be considered equivalentto raising the products price to that of the nexthighest class).

    However, using

    price

    as

    a

    directmechanism to match demand with capacity is an

    important

    enough

    practical

    problem

    to

    merit

    specialtreatment. Dynamic pricing has gained significanttraction lately, particularly in retailing (i.e., mark-down pricing), e-commerce, and even manufactur-ing (e.g., Fords offering of incentives at its autodealers).The

    key

    is

    to

    find

    a

    good

    predictive

    demandmodel: At price p, what is the expected demandd(p) for the product? Demand models may be linear(d(p) = a-bp), exponential (i.e., constant elastici-ty), logit (i.e., S-curve), or discrete-choice. Thereare many vendors of dynamic pricing software, andsoftware calibrates the demand models using histor-ical point-of-sale

    data.

    In

    addition,

    dataon

    availableinventories is necessary for the price-optimizationalgorithm. Different price-optimization algorithmsareembedded in these packages based on non-linearand dynamic programming.

    7. Conclusion

    Supply chain management is a fertile area for theapplication of analytics techniques, which has his-torically been the case through the use of operations

    research, particularly linear programming andoptimization. For example, inventory theory is morethan 50 years old, and there were significantcontributions to production planning in the 1980s.Therefore, analytics

    in

    supply

    chain

    management

    isnot new. More recent applications include the inte-gration of price analytics and supply chain manage-

    ment in

    the

    field

    of

    revenue

    management,

    for

    whichthe problem revolves around managing demand inan environment with fixed and perishable capacity.Revenue management research and practice (par-ticularly inmanufacturing) is relatively new becausemany demand models can only be calibrated withsignificant amounts of data, which just recentlybecame available from modern ERP systems andweb technologies.With

    big

    data,

    new

    opportunities

    arise.

    I haveheard consultants praising the potential of harness-ing social networks for supply chain management,for example,

    by

    detecting

    local

    trends in

    demand

    to

    adjust inventories and prices. There is indeed po-tential there, although many firms still struggle tomatch basic supply and demand in a world withincreased product

    proliferation,

    competition,

    andglobalization (i.e., longer lead times). Among otherbenefits, big data has the potential to improvedemand forecasting

    methods,

    detect

    supply

    chaindisruptions, and improve communications in supplychains that are often global (see Table 7).

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    Table

    7.

    Additional

    information

    on

    analytics

    techniques for supply chain management

    General overview: Snyder and Shen (2011) Network

    design:

    Funaki

    (2009) Auctions: Krishna (2002) Sales and operations planning: Jacobs, Berry,Whybark, and Vollmann (2011)

    Transportation

    and

    distribution

    planning:

    Ahuja,Magnanti, and Orlin (1993) Inventory management: Zipkin (2000)Dynamic pricing and revenue management: Talluriand Van Ryzin (2004)

    Manufacturing scheduling: Pinedo (2008) Workforce scheduling: Campbell (2009)

    604 G.C. Souza

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