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  <xs:element id="it_ConsultingMember" abstract="true" name="ConsultingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_BusinessCombinationDeferredConsideration" abstract="false" name="BusinessCombinationDeferredConsideration" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_NonExecutiveMember" abstract="true" name="NonExecutiveMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_SeniorNotesDue2030Member" abstract="true" name="SeniorNotesDue2030Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_EffectiveIncomeTaxRateReconciliationGlobalIntangibleLowTaxedIncomeNetOfForeignTaxCredits" abstract="false" name="EffectiveIncomeTaxRateReconciliationGlobalIntangibleLowTaxedIncomeNetOfForeignTaxCredits" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="it_OperatingLeaseRightOfUseAssetReductionInCarryingAmount" abstract="false" name="OperatingLeaseRightOfUseAssetReductionInCarryingAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_VariableRateComponentsDomain" abstract="true" name="VariableRateComponentsDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_OperatingLossCarryforwardsExpirationPeriod" abstract="false" name="OperatingLossCarryforwardsExpirationPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_OtherLiabilitiesNoncurrentOther" abstract="false" name="OtherLiabilitiesNoncurrentOther" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedandExercisableNumber" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedandExercisableNumber" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="it_EffectiveIncomeTaxRateReconciliationForeignDerivedIntangibleIncomePercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationForeignDerivedIntangibleIncomePercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="it_AveragemarketpricepershareofCommonStockduringtheyear" abstract="false" name="AveragemarketpricepershareofCommonStockduringtheyear" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="it_DebtInstrumentRedemptionOptionThreeMember" abstract="true" name="DebtInstrumentRedemptionOptionThreeMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_VariableRateComponentTwoMember" abstract="true" name="VariableRateComponentTwoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_StockRepurchaseProgramAdditionalAuthorizedAmount" abstract="false" name="StockRepurchaseProgramAdditionalAuthorizedAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsVestedandExpectedtoVestExercisableWeightedAverageExercisePrice." abstract="false" name="SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsVestedandExpectedtoVestExercisableWeightedAverageExercisePrice." nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="it_OtherInternationalMember" abstract="true" name="OtherInternationalMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_OtherIncomeAndExpenseMember" abstract="true" name="OtherIncomeAndExpenseMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_DeferredTaxAssetsLeasingArrangements" abstract="false" name="DeferredTaxAssetsLeasingArrangements" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnvestedConversionsInPeriodWeightedAverageGrantDateFairValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnvestedConversionsInPeriodWeightedAverageGrantDateFairValue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="it_BusinessCombinationAcquisitionandIntegrationRelatedCosts" abstract="false" name="BusinessCombinationAcquisitionandIntegrationRelatedCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_DeferredTaxAssetsAccruedExpenses" abstract="false" name="DeferredTaxAssetsAccruedExpenses" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnvestedConversionsInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnvestedConversionsInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="it_DeferredTaxAssetsOperatingLossAndTaxCreditCarryforwards" abstract="false" name="DeferredTaxAssetsOperatingLossAndTaxCreditCarryforwards" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_OperatingLeaseCostSubleasingActivities" abstract="false" name="OperatingLeaseCostSubleasingActivities" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_CommonStockEquivalentsMember" abstract="true" name="CommonStockEquivalentsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_DebtInstrumentRedemptionOptionOneMember" abstract="true" name="DebtInstrumentRedemptionOptionOneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_FederalReserveBoardOfNewYorkRateMember" abstract="true" name="FederalReserveBoardOfNewYorkRateMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_SeniorNotesDue2029Member" abstract="true" name="SeniorNotesDue2029Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_BusinessCombinationFutureCompensationExpense" abstract="false" name="BusinessCombinationFutureCompensationExpense" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_AssetsAndLiabilitiesLeasesTableTextBlock" abstract="false" name="AssetsAndLiabilitiesLeasesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="it_EffectiveIncomeTaxRateReconciliationIntercompanySaleOfIntellectualPropertyPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationIntercompanySaleOfIntellectualPropertyPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="it_EventsMember" abstract="true" name="EventsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementbyShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingIntrinsicValue." abstract="false" name="ShareBasedCompensationArrangementbyShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingIntrinsicValue." nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_AmortizationOfDeferredSwapLosses" abstract="false" name="AmortizationOfDeferredSwapLosses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_IncomeTaxTable" abstract="true" name="IncomeTaxTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementbyShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageRemainingContractualTerm." abstract="false" name="ShareBasedCompensationArrangementbyShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageRemainingContractualTerm." nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_ConferencesMember" abstract="true" name="ConferencesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByEmployeeStockPurchasePlanStockPurchasesAsPercentageOfEmployeeCompensationMaximum" abstract="false" name="ShareBasedCompensationArrangementByEmployeeStockPurchasePlanStockPurchasesAsPercentageOfEmployeeCompensationMaximum" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="it_IncomeTaxExpenseBenefitbeforeOther" abstract="false" name="IncomeTaxExpenseBenefitbeforeOther" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_LesseeOperatingLeaseLeaseNotYetCommencedTerm" abstract="false" name="LesseeOperatingLeaseLeaseNotYetCommencedTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_EconomicDevelopmentLoan1Member" abstract="true" name="EconomicDevelopmentLoan1Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_AcquisitionandIntegrationChargesMember" abstract="true" name="AcquisitionandIntegrationChargesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_ExpireOverNextTwentyYearsMember" abstract="true" name="ExpireOverNextTwentyYearsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_RestrictedEquityAwardTypeAxis" abstract="true" name="RestrictedEquityAwardTypeAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="it_DefinedBenefitPlanReinsuranceAsset" abstract="false" name="DefinedBenefitPlanReinsuranceAsset" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_FloatingEurodollarBaseRate" abstract="false" name="FloatingEurodollarBaseRate" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="it_SegmentReportingInformationPercentOfSubscriptionContractsBillableUponSigningForTwelveMonthsOfService" abstract="false" name="SegmentReportingInformationPercentOfSubscriptionContractsBillableUponSigningForTwelveMonthsOfService" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
</xs:schema>
