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  <xs:element id="it_UnrecognizedTaxBenefitsthatWouldResultAdjustmentstoOtherTaxAccounts" abstract="false" name="UnrecognizedTaxBenefitsthatWouldResultAdjustmentstoOtherTaxAccounts" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_BenefitFromStockTransactionsWithEmployeesUsedToIncreaseEquityMember" abstract="true" name="BenefitFromStockTransactionsWithEmployeesUsedToIncreaseEquityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_OperatingLeasesConcentrationPercentageOfPayments" abstract="false" name="OperatingLeasesConcentrationPercentageOfPayments" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_GartnerResearchProductsMember" abstract="true" name="GartnerResearchProductsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_ConferencesMember" abstract="true" name="ConferencesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_BusinessCombinationRecognitionOfCompensationExpenseTerm" abstract="false" name="BusinessCombinationRecognitionOfCompensationExpenseTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_DebtInstrumentRedemptionOptionDomain" abstract="true" name="DebtInstrumentRedemptionOptionDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_DefinedBenefitPlanActuarialGainsLosses" abstract="false" name="DefinedBenefitPlanActuarialGainsLosses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_OperatingLossCarryforwardsExpirationPeriod" abstract="false" name="OperatingLossCarryforwardsExpirationPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_OtherLongTermDebtMember" abstract="true" name="OtherLongTermDebtMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_ChicagoIllinoisMember" abstract="true" name="ChicagoIllinoisMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedInPeriodWeightedAverageRemainingContractualTerm" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedInPeriodWeightedAverageRemainingContractualTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_FiniteLivedIntangibleAssetsReclassifiedAsHeldForSale" abstract="false" name="FiniteLivedIntangibleAssetsReclassifiedAsHeldForSale" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_ServiceBasedAwardsMember" abstract="true" name="ServiceBasedAwardsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_NumeratorAbstract" abstract="true" name="NumeratorAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_PeriodAxis" abstract="true" name="PeriodAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="it_DeferredTaxAssetsIntangibleAssetsTaxBasis" abstract="false" name="DeferredTaxAssetsIntangibleAssetsTaxBasis" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_CorporateAndReconcilingItemsMember" abstract="true" name="CorporateAndReconcilingItemsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_PlanLiabilitiesMember" abstract="true" name="PlanLiabilitiesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnvestedConversionsInPeriodWeightedAverageGrantDateFairValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnvestedConversionsInPeriodWeightedAverageGrantDateFairValue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="it_RightOfUseAssetsMember" abstract="true" name="RightOfUseAssetsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_ConsultingMember" abstract="true" name="ConsultingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_SeniorNotesDue2030Member" abstract="true" name="SeniorNotesDue2030Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_PlanAssetsMember" abstract="true" name="PlanAssetsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_UnrecognizedTaxBenefitsReductionsResultingfromSettlementswithTaxingAuthoritiesandLapseofApplicableStatuteofLimitations" abstract="false" name="UnrecognizedTaxBenefitsReductionsResultingfromSettlementswithTaxingAuthoritiesandLapseofApplicableStatuteofLimitations" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_RetirementEligibleEmployeesEquityAwardMember" abstract="true" name="RetirementEligibleEmployeesEquityAwardMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_LesseeOperatingLeaseLeaseNotYetCommencedUndiscountedLeasePayments" abstract="false" name="LesseeOperatingLeaseLeaseNotYetCommencedUndiscountedLeasePayments" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_TalentNeuronMember" abstract="true" name="TalentNeuronMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_OtherInternationalMember" abstract="true" name="OtherInternationalMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_BusinessandSignificantAccountingPoliciesTable" abstract="true" name="BusinessandSignificantAccountingPoliciesTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <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_EventsMember" abstract="true" name="EventsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1: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_SegmentReportingInformationPercentofTargetBonusChargesAllocatedtoSegments" abstract="false" name="SegmentReportingInformationPercentofTargetBonusChargesAllocatedtoSegments" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <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_AmountsRecordedInTheConsolidatedBalanceSheetsForThePlansAbstract" abstract="true" name="AmountsRecordedInTheConsolidatedBalanceSheetsForThePlansAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_EmployeeStockPurchasePlanMaximumNumberofSharesthatMaybePurchasebyEligibleParticipants" abstract="false" name="EmployeeStockPurchasePlanMaximumNumberofSharesthatMaybePurchasebyEligibleParticipants" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="it_RestrictedEquityAwardTypeAxis" abstract="true" name="RestrictedEquityAwardTypeAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpiryPeriodFromDateOfGrant" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardExpiryPeriodFromDateOfGrant" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsVestedandExpectedtoVestExercisableWeightedAverageExercisePrice." abstract="false" name="SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsVestedandExpectedtoVestExercisableWeightedAverageExercisePrice." nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="it_NonExecutiveMember" abstract="true" name="NonExecutiveMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_TermLoanFacilityMember" abstract="true" name="TermLoanFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_BusinessandSignificantAccountingPoliciesLineItems" abstract="true" name="BusinessandSignificantAccountingPoliciesLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <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_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostFutureExpectedLongtermRateOfReturnOnPlanAssets" abstract="false" name="DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostFutureExpectedLongtermRateOfReturnOnPlanAssets" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFiniteLivedIntangibleAssetsAndGoodwill" abstract="false" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFiniteLivedIntangibleAssetsAndGoodwill" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedandExpectedtoVestExercisableAggregateIntrinsicValue." abstract="false" name="SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedandExpectedtoVestExercisableAggregateIntrinsicValue." nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_ForeignCurrencyExchangeContractsMember" abstract="true" name="ForeignCurrencyExchangeContractsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_EmployeeStockPurchasePlanMember" abstract="true" name="EmployeeStockPurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsVestedExpectedtoVestandExercisableWeightedAverageGrantDateFairValue." abstract="false" name="SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsVestedExpectedtoVestandExercisableWeightedAverageGrantDateFairValue." nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <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_TaxCreditCarryforwardExpirationPeriod" abstract="false" name="TaxCreditCarryforwardExpirationPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_Denominator1Abstract" abstract="true" name="Denominator1Abstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_ConnecticutEconomicDevelopmentProgramMember" abstract="true" name="ConnecticutEconomicDevelopmentProgramMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_ExpireWithinOneToFiveYearsMember" abstract="true" name="ExpireWithinOneToFiveYearsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="it_CashPaidDuringThePeriodForAbstract" abstract="true" name="CashPaidDuringThePeriodForAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_ResearchRevenueMember" abstract="true" name="ResearchRevenueMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_LiabilitiesAbstract0" abstract="true" name="LiabilitiesAbstract0" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_InterestExpenseandOtherNonoperatingIncome" abstract="false" name="InterestExpenseandOtherNonoperatingIncome" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_EffectiveIncomeTaxRateReconciliationChangesInTaxLawsPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationChangesInTaxLawsPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumShareValueAuthorizedForPurchaseUnderEmployeeStockPurchasePlan" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumShareValueAuthorizedForPurchaseUnderEmployeeStockPurchasePlan" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerm" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_FederalReserveBoardOfNewYorkRateMember" abstract="true" name="FederalReserveBoardOfNewYorkRateMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_UnvestedMember" abstract="true" name="UnvestedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_LongLivedAssets1Abstract" abstract="true" name="LongLivedAssets1Abstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_ExpireWithinSixToFifteenYearsMember" abstract="true" name="ExpireWithinSixToFifteenYearsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <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_AveragemarketpricepershareofCommonStockduringtheyear" abstract="false" name="AveragemarketpricepershareofCommonStockduringtheyear" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="it_GoodwillReclassifiedAsHeldForSale" abstract="false" name="GoodwillReclassifiedAsHeldForSale" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_NetIncomePerShareBasicAndDilutedAbstract" abstract="true" name="NetIncomePerShareBasicAndDilutedAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_ChangesInAssetsAndLiabilitiesAbstract" abstract="true" name="ChangesInAssetsAndLiabilitiesAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_DebtInstrumentRedemptionOptionOneMember" abstract="true" name="DebtInstrumentRedemptionOptionOneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisesInPeriodWeightedAverageGrantDateFairValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisesInPeriodWeightedAverageGrantDateFairValue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="it_VariableRateComponentsDomain" abstract="true" name="VariableRateComponentsDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_A2020CreditAgreementMember" abstract="true" name="A2020CreditAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_CommonStockOutstandingRollForwardRollForward" abstract="true" name="CommonStockOutstandingRollForwardRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageExercisePrice" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="it_DebtInstrumentRedemptionOptionAxis" abstract="true" name="DebtInstrumentRedemptionOptionAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisablePricePercentageOfClosingPriceOfAnotherClassOfStock" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisablePricePercentageOfClosingPriceOfAnotherClassOfStock" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_ResearchSegmentMember" abstract="true" name="ResearchSegmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_FloatingEurodollarBaseRate" abstract="false" name="FloatingEurodollarBaseRate" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_SeniorNotesDue2029Member" abstract="true" name="SeniorNotesDue2029Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_BenefitExpenseRelatingToInterestRateSwapUsedToIncreaseDecreaseEquityMember" abstract="true" name="BenefitExpenseRelatingToInterestRateSwapUsedToIncreaseDecreaseEquityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_CommonStockNumberofVotesperShare" abstract="false" name="CommonStockNumberofVotesperShare" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="it_VariableRateComponentOneMember" abstract="true" name="VariableRateComponentOneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <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_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisesInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisesInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="it_EuropeMiddleEastAfricaMember" abstract="true" name="EuropeMiddleEastAfricaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_PulseQAIncMember" abstract="true" name="PulseQAIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnvestedConversionsInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndUnvestedConversionsInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisesInPeriodWeightedAverageExercisePrice" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisesInPeriodWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByEmployeeStockPurchasePlanStockPurchasesAsPercentageOfEmployeeCompensationMaximum" abstract="false" name="ShareBasedCompensationArrangementByEmployeeStockPurchasePlanStockPurchasesAsPercentageOfEmployeeCompensationMaximum" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndReleasedInPeriodWeightedAverageGrantDateFairValue" abstract="false" name="SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndReleasedInPeriodWeightedAverageGrantDateFairValue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="it_DeferredTaxLiabilitiesDepreciation" abstract="false" name="DeferredTaxLiabilitiesDepreciation" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementbyShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageRemainingContractualTerm." abstract="false" name="ShareBasedCompensationArrangementbyShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageRemainingContractualTerm." nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_BaseFeePercentage" abstract="false" name="BaseFeePercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_RestrictedEquityAwardTypeDomain" abstract="true" name="RestrictedEquityAwardTypeDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_EarningsPerShareBasicAndDilutedEPSAbstract" abstract="true" name="EarningsPerShareBasicAndDilutedEPSAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_EffectiveIncomeTaxRateReconciliationLimitationOfExecutiveCompensationPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationLimitationOfExecutiveCompensationPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_PeriodDomain" abstract="true" name="PeriodDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_SecuredOvernightFinancingRateSOFRMember" abstract="true" name="SecuredOvernightFinancingRateSOFRMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <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_EffectiveIncomeTaxRateReconciliationIntercompanySaleOfIntellectualPropertyPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationIntercompanySaleOfIntellectualPropertyPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_AssetsAndLiabilitiesLeasesTableTextBlock" abstract="false" name="AssetsAndLiabilitiesLeasesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="it_EconomicDevelopmentLoan1Member" abstract="true" name="EconomicDevelopmentLoan1Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_VariableRateComponentsAxis" abstract="true" name="VariableRateComponentsAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="it_IncomeTaxTable" abstract="true" name="IncomeTaxTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="it_LesseeOperatingLeaseOptiontoTerminateTerm" abstract="false" name="LesseeOperatingLeaseOptiontoTerminateTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_EffectiveIncomeTaxRateReconciliationIntercompanySaleOfIntellectualPropertyAmount" abstract="false" name="EffectiveIncomeTaxRateReconciliationIntercompanySaleOfIntellectualPropertyAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_TaxesPayableNoncurrent" abstract="false" name="TaxesPayableNoncurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeLossDeferredActuarialLossWeightedAverageAmortizationPeriod" abstract="false" name="DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeLossDeferredActuarialLossWeightedAverageAmortizationPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="it_SegmentReportingInformationPercentOfSubscriptionContractsBillableUponSigningForTwelveMonthsOfService" abstract="false" name="SegmentReportingInformationPercentOfSubscriptionContractsBillableUponSigningForTwelveMonthsOfService" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsTargetPerformancePercentage" abstract="false" name="ShareBasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsTargetPerformancePercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_UnitedStatesAndCanadaMember" abstract="true" name="UnitedStatesAndCanadaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_SeniorNotesDue2028Member" abstract="true" name="SeniorNotesDue2028Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <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_IncomeTaxLineItems" abstract="true" name="IncomeTaxLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsNonvestedWeightedAverageRemainingContractualTermRollForward" abstract="true" name="SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsNonvestedWeightedAverageRemainingContractualTermRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_ExpireWithinSixteenToTwentyYearsMember" abstract="true" name="ExpireWithinSixteenToTwentyYearsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageExercisePriceRollForward" abstract="true" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageExercisePriceRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_DebtInstrumentIssuePricePercentage" abstract="false" name="DebtInstrumentIssuePricePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <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_AuditInformationAbstract" abstract="true" name="AuditInformationAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <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_DeferredTaxBenefitExpenseAbstract" abstract="true" name="DeferredTaxBenefitExpenseAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <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_ExpireOverNextTwentyYearsMember" abstract="true" name="ExpireOverNextTwentyYearsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_IncomeTaxReconciliationDispositionOfAssetsIncomeTaxExpenseBenefitPerShare" abstract="false" name="IncomeTaxReconciliationDispositionOfAssetsIncomeTaxExpenseBenefitPerShare" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="it_AssetsAbstract00" abstract="true" name="AssetsAbstract00" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardCommonSharesPerVestedAward" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardCommonSharesPerVestedAward" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="it_DebtInstrumentAdditionalInterestaboveBaseRate" abstract="false" name="DebtInstrumentAdditionalInterestaboveBaseRate" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="it_BenefitExpenseRelatingToDefinedBenefitPensionAdjustmentsUsedToIncreaseDecreaseEquityMember" abstract="true" name="BenefitExpenseRelatingToDefinedBenefitPensionAdjustmentsUsedToIncreaseDecreaseEquityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageExercisePrice" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageExercisePrice" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="it_EquipmentAndFurnitureMember" abstract="true" name="EquipmentAndFurnitureMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_CommonStockEquivalentsMember" abstract="true" name="CommonStockEquivalentsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_FiniteLivedIntangibleAssetsFullyAmortizedIntangibles" abstract="false" name="FiniteLivedIntangibleAssetsFullyAmortizedIntangibles" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="it_CarriedForwardIndefinitelyMember" abstract="true" name="CarriedForwardIndefinitelyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="it_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndReleasedInPeriod" abstract="false" name="SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndReleasedInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <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_NumberofEnterprisesServed" abstract="false" name="NumberofEnterprisesServed" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
</xs:schema>
