<?xml version="1.0" encoding="utf-8"?>
<!--XBRL document created with Toppan Merrill Bridge  10.7.0.1 -->
<!--Based on XBRL 2.1-->
<!--Created on: 8/6/2024 9:14:06 PM-->
<!--Modified on: 8/6/2024 9:14:06 PM-->
<xsd:schema xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xl="http://www.xbrl.org/2003/XLink" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:ref="http://www.xbrl.org/2006/ref" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:utr="http://www.xbrl.org/2009/utr" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" targetNamespace="http://www.informationsg.com/20240630" attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:country="http://xbrl.sec.gov/country/2024" xmlns:us-gaap="http://fasb.org/us-gaap/2024" xmlns:us-types="http://fasb.org/us-types/2024" xmlns:negated="http://www.xbrl.org/2009/role/negated" xmlns:srt-types="http://fasb.org/srt-types/2024" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2022-03-31" xmlns:iii="http://www.informationsg.com/20240630" xmlns:enum2="http://xbrl.org/2020/extensible-enumerations-2.0" xmlns:currency="http://xbrl.sec.gov/currency/2024" xmlns:us-roles="http://fasb.org/us-roles/2024" xmlns:sic="http://xbrl.sec.gov/sic/2024" xmlns:srt-roles="http://fasb.org/srt-roles/2024" xmlns:stpr="http://xbrl.sec.gov/stpr/2024" xmlns:exch="http://xbrl.sec.gov/exch/2024" xmlns:naics="http://xbrl.sec.gov/naics/2024" xmlns:attributeFormDefault="unqualified" xmlns:srt="http://fasb.org/srt/2024" xmlns:deprecated="http://www.xbrl.org/2009/role/deprecated" xmlns:net="http://www.xbrl.org/2009/role/net" xmlns:dei="http://xbrl.sec.gov/dei/2024" xmlns:dtr="http://www.xbrl.org/2009/dtr" xmlns:xbrldi="http://xbrl.org/2006/xbrldi" xmlns:us-gaap-ebp="http://fasb.org/us-gaap-ebp/2024" xmlns:ecd="http://xbrl.sec.gov/ecd/2024" xmlns:ecd-sub="http://xbrl.sec.gov/ecd-sub/2024">
  <xsd:annotation>
    <xsd:appinfo>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureStandardAndCustomAxisDomainDefaults" id="DisclosureStandardAndCustomAxisDomainDefaults">
        <link:definition>99900 - Disclosure - Standard And Custom Axis Domain Defaults</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/StatementCondensedConsolidatedBalanceSheets" id="StatementCondensedConsolidatedBalanceSheets">
        <link:definition>995200100 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/StatementCondensedConsolidatedStatementsOfIncomeAndComprehensiveIncome" id="StatementCondensedConsolidatedStatementsOfIncomeAndComprehensiveIncome">
        <link:definition>995200200 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/StatementCondensedConsolidatedStatementsOfCashFlows" id="StatementCondensedConsolidatedStatementsOfCashFlows">
        <link:definition>995200400 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureAcquisitionsTotalAllocablePurchasePriceDetails" id="DisclosureAcquisitionsTotalAllocablePurchasePriceDetails">
        <link:definition>99940401 - Disclosure - ACQUISITIONS - Total allocable purchase price (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureAcquisitionsRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAndAcquisitionCostsDetails" id="DisclosureAcquisitionsRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAndAcquisitionCostsDetails">
        <link:definition>99940402 - Disclosure - ACQUISITIONS - Recognized identifiable assets acquired and liabilities assumed and acquisition costs (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureNetIncomePerCommonShareComputationDetails" id="DisclosureNetIncomePerCommonShareComputationDetails">
        <link:definition>99940602 - Disclosure - NET INCOME PER COMMON SHARE - Computation (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureFinancingArrangementsAndLongTermDebtLongTermDebtDetailsCalc2" id="DisclosureFinancingArrangementsAndLongTermDebtLongTermDebtDetailsCalc2">
        <link:definition>41201 - Disclosure - FINANCING ARRANGEMENTS AND LONG-TERM DEBT - Long-term Debt (Details) calc2</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DocumentDocumentAndEntityInformation" id="DocumentDocumentAndEntityInformation">
        <link:definition>995200090 - Document - Document And Entity Information</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/StatementCondensedConsolidatedBalanceSheetsParenthetical" id="StatementCondensedConsolidatedBalanceSheetsParenthetical">
        <link:definition>995200105 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/StatementCondensedConsolidatedStatementsOfIncomeAndComprehensiveIncomeParenthetical" id="StatementCondensedConsolidatedStatementsOfIncomeAndComprehensiveIncomeParenthetical">
        <link:definition>995200205 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/StatementCondensedConsolidatedStatementsOfStockholdersEquity" id="StatementCondensedConsolidatedStatementsOfStockholdersEquity">
        <link:definition>995200300 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/StatementCondensedConsolidatedStatementsOfStockholdersEquityParenthetical" id="StatementCondensedConsolidatedStatementsOfStockholdersEquityParenthetical">
        <link:definition>995200305 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureDescriptionOfOrganizationAndBusinessOperations" id="DisclosureDescriptionOfOrganizationAndBusinessOperations">
        <link:definition>995210101 - Disclosure - DESCRIPTION OF ORGANIZATION AND BUSINESS OPERATIONS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureBasisOfPresentation" id="DisclosureBasisOfPresentation">
        <link:definition>995210201 - Disclosure - BASIS OF PRESENTATION</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureSummaryOfSignificantAccountingPolicies" id="DisclosureSummaryOfSignificantAccountingPolicies">
        <link:definition>995210301 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureAcquisitions" id="DisclosureAcquisitions">
        <link:definition>995210401 - Disclosure - ACQUISITIONS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureNetIncomePerCommonShare" id="DisclosureNetIncomePerCommonShare">
        <link:definition>995210601 - Disclosure - NET INCOME PER COMMON SHARE</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureIncomeTaxes" id="DisclosureIncomeTaxes">
        <link:definition>995210701 - Disclosure - INCOME TAXES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureCommitmentsAndContingencies" id="DisclosureCommitmentsAndContingencies">
        <link:definition>995210801 - Disclosure - COMMITMENTS AND CONTINGENCIES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureSegmentAndGeographicalInformation" id="DisclosureSegmentAndGeographicalInformation">
        <link:definition>995210901 - Disclosure - SEGMENT AND GEOGRAPHICAL INFORMATION</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureFinancingArrangementsAndLongTermDebt" id="DisclosureFinancingArrangementsAndLongTermDebt">
        <link:definition>995211001 - Disclosure - FINANCING ARRANGEMENTS AND LONG-TERM DEBT</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureSubsequentEvents" id="DisclosureSubsequentEvents">
        <link:definition>995211101 - Disclosure - SUBSEQUENT EVENTS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies" id="DisclosureSummaryOfSignificantAccountingPoliciesPolicies">
        <link:definition>99920302 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureSummaryOfSignificantAccountingPoliciesTables" id="DisclosureSummaryOfSignificantAccountingPoliciesTables">
        <link:definition>99930303 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureAcquisitionsTables" id="DisclosureAcquisitionsTables">
        <link:definition>99930403 - Disclosure - ACQUISITIONS (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureNetIncomePerCommonShareTables" id="DisclosureNetIncomePerCommonShareTables">
        <link:definition>99930603 - Disclosure - NET INCOME PER COMMON SHARE (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureSegmentAndGeographicalInformationTables" id="DisclosureSegmentAndGeographicalInformationTables">
        <link:definition>99930903 - Disclosure - SEGMENT AND GEOGRAPHICAL INFORMATION (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureDescriptionOfOrganizationAndBusinessOperationsDetails" id="DisclosureDescriptionOfOrganizationAndBusinessOperationsDetails">
        <link:definition>99940101 - Disclosure - DESCRIPTION OF ORGANIZATION AND BUSINESS OPERATIONS (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureBasisOfPresentationDetails" id="DisclosureBasisOfPresentationDetails">
        <link:definition>99940201 - Disclosure - BASIS OF PRESENTATION (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetails" id="DisclosureSummaryOfSignificantAccountingPoliciesDetails">
        <link:definition>99940301 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureAcquisitionsAmortizableIntangibleAssetsAndPeriodDetails" id="DisclosureAcquisitionsAmortizableIntangibleAssetsAndPeriodDetails">
        <link:definition>99940403 - Disclosure - ACQUISITIONS - Amortizable intangible assets and period (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureNetIncomePerCommonShareAntidilutiveSecuritiesDetails" id="DisclosureNetIncomePerCommonShareAntidilutiveSecuritiesDetails">
        <link:definition>99940601 - Disclosure - NET INCOME PER COMMON SHARE - Antidilutive Securities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureIncomeTaxesDetails" id="DisclosureIncomeTaxesDetails">
        <link:definition>99940701 - Disclosure - INCOME TAXES (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureCommitmentsAndContingenciesDetails" id="DisclosureCommitmentsAndContingenciesDetails">
        <link:definition>99940801 - Disclosure - COMMITMENTS AND CONTINGENCIES (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureSegmentAndGeographicalInformationDetails" id="DisclosureSegmentAndGeographicalInformationDetails">
        <link:definition>99940901 - Disclosure - SEGMENT AND GEOGRAPHICAL INFORMATION (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureFinancingArrangementsAndLongTermDebtDetails" id="DisclosureFinancingArrangementsAndLongTermDebtDetails">
        <link:definition>99941001 - Disclosure - FINANCING ARRANGEMENTS AND LONG-TERM DEBT (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureSubsequentEventsDetails" id="DisclosureSubsequentEventsDetails">
        <link:definition>99941101 - Disclosure - SUBSEQUENT EVENTS (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureRevenue" id="DisclosureRevenue">
        <link:definition>995210501 - Disclosure - REVENUE</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureRevenueTables" id="DisclosureRevenueTables">
        <link:definition>99930503 - Disclosure - REVENUE (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureRevenueContractBalancesDetails" id="DisclosureRevenueContractBalancesDetails">
        <link:definition>99940501 - Disclosure - REVENUE - Contract Balances (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.informationsg.com/role/DisclosureRevenueNarrativeDetails" id="DisclosureRevenueNarrativeDetails">
        <link:definition>99940502 - Disclosure - REVENUE - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:linkbaseRef xlink:type="simple" xlink:href="iii-20240630_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="iii-20240630_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="iii-20240630_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
      <link:linkbaseRef xlink:type="simple" xlink:href="iii-20240630_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" />
    </xsd:appinfo>
  </xsd:annotation>
  <xsd:import namespace="https://xbrl.org/2023/calculation-1.1" schemaLocation="https://www.xbrl.org/2023/calculation-1.1.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/ecd/2024" schemaLocation="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/dei/2024" schemaLocation="https://xbrl.sec.gov/dei/2024/dei-2024.xsd" />
  <xsd:import namespace="http://fasb.org/us-roles/2024" schemaLocation="https://xbrl.fasb.org/us-gaap/2024/elts/us-roles-2024.xsd" />
  <xsd:import namespace="http://www.xbrl.org/dtr/type/2022-03-31" schemaLocation="https://www.xbrl.org/dtr/type/2022-03-31/types.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2009/role/negated" schemaLocation="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
  <xsd:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" />
  <xsd:import namespace="http://fasb.org/us-gaap/2024" schemaLocation="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd" />
  <xsd:import namespace="http://fasb.org/srt/2024" schemaLocation="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/ecd-sub/2024" schemaLocation="https://xbrl.sec.gov/ecd/2024/ecd-sub-2024.xsd" />
  <xsd:element name="BasisOfPresentationDisclosureAbstract" id="iii_BasisOfPresentationDisclosureAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="BasisOfPresentationDisclosureTextBlock" id="iii_BasisOfPresentationDisclosureTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="FinancingArrangementsAndLongTermDebtDisclosureAbstract" id="iii_FinancingArrangementsAndLongTermDebtDisclosureAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="FinancingArrangementsAndLongTermDebtDisclosureTextBlock" id="iii_FinancingArrangementsAndLongTermDebtDisclosureTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="NumberOfClients" id="iii_NumberOfClients" type="xbrli:integerItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="instant" />
  <xsd:element name="StockIssuedDuringPeriodValueShareBasedCompensationTreasuryStockReissued" id="iii_StockIssuedDuringPeriodValueShareBasedCompensationTreasuryStockReissued" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" abstract="false" nillable="true" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="iii_IssuanceOfTreasuryStockForESPPAndVestedRestrictedStockAwardsAndStockAppreciationRights" name="IssuanceOfTreasuryStockForESPPAndVestedRestrictedStockAwardsAndStockAppreciationRights" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <xsd:element name="DefinedContributionPlanDateAxis" id="iii_DefinedContributionPlanDateAxis" type="xbrli:stringItemType" substitutionGroup="xbrldt:dimensionItem" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="DefinedContributionPlanDateDomain" id="iii_DefinedContributionPlanDateDomain" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element id="iii_BusinessCombinationContingentConsiderationLiabilityAccretion" name="BusinessCombinationContingentConsiderationLiabilityAccretion" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <xsd:element id="iii_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationRollForward" name="BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationRollForward" nillable="true" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="iii_DeferredIncomeTaxExpenseBenefitAdjustments" name="DeferredIncomeTaxExpenseBenefitAdjustments" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <xsd:element id="iii_DeferredTaxBenefitExpenseFromStockIssuances" name="DeferredTaxBenefitExpenseFromStockIssuances" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <xsd:element id="iii_AccountsReceivableAndContractAssetsNet" name="AccountsReceivableAndContractAssetsNet" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element id="iii_IncreaseDecreaseInAccountsReceivableAndContractWithCustomerAsset" name="IncreaseDecreaseInAccountsReceivableAndContractWithCustomerAsset" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <xsd:element id="iii_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesContractLiabilities" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesContractLiabilities" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" />
  <xsd:element id="iii_BusinessCombinationContingentConsiderationArrangementsLiabilityAccrued" name="BusinessCombinationContingentConsiderationArrangementsLiabilityAccrued" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <xsd:element id="iii_NumberOfClientsFromTop100Enterprises" name="NumberOfClientsFromTop100Enterprises" nillable="true" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" />
  <xsd:element id="iii_AdjustmentsToAdditionalPaidInCapitalAccruedDividendsOnUnvestedShares" name="AdjustmentsToAdditionalPaidInCapitalAccruedDividendsOnUnvestedShares" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <xsd:element name="AcquisitionsTextBlock" id="iii_AcquisitionsTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="IncreaseDecreaseInAccruedLiabilitiesAndOtherLiabilities" id="iii_IncreaseDecreaseInAccruedLiabilitiesAndOtherLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="debit" />
  <xsd:element name="Change4GrowthLLCMember" id="iii_Change4GrowthLLCMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="Change4GrowthAcquisitionMember" id="iii_Change4GrowthAcquisitionMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="PaymentsToAcquireBusinessesExcludingAccruedExcessWorkingCapitalAdjustment" id="iii_PaymentsToAcquireBusinessesExcludingAccruedExcessWorkingCapitalAdjustment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="PaymentsToAcquireBusinessesAccruedExcessWorkingCapitalAdjustment" id="iii_PaymentsToAcquireBusinessesAccruedExcessWorkingCapitalAdjustment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccountsReceivableAndContractAssets" id="iii_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccountsReceivableAndContractAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="instant" abstract="false" xbrli:balance="debit" />
  <xsd:element name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccountsPayableAndAccruedExpense" id="iii_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccountsPayableAndAccruedExpense" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="instant" abstract="false" xbrli:balance="credit" />
  <xsd:element name="CreditAgreement2023Member" id="iii_CreditAgreement2023Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="DebtInstrumentCreditSpreadAdjustment" id="iii_DebtInstrumentCreditSpreadAdjustment" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="DividendsCommonStockCashPaid" id="iii_DividendsCommonStockCashPaid" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="debit" />
  <xsd:element name="DividendsCommonStockPayable" id="iii_DividendsCommonStockPayable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="VentanaResearchIncMember" id="iii_VentanaResearchIncMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="Rule10b51ArrangementModifiedFlag" id="iii_Rule10b51ArrangementModifiedFlag" type="xbrli:booleanItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="NonRule10b51ArrangementModified" id="iii_NonRule10b51ArrangementModified" type="xbrli:booleanItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" />
  <xsd:element name="RevenueFromContractWithCustomerExcludingAssessedTaxIncorrectlyRecognized" id="iii_RevenueFromContractWithCustomerExcludingAssessedTaxIncorrectlyRecognized" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
</xsd:schema>
