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<?xml version="1.0" encoding="windows-1252"?> |
<!-- DFIN - https://www.dfinsolutions.com/ --> |
<!-- CTU Version: Release 2020-5 Build:20200707.2 --> |
<!-- Creation date: 9/14/2020 11:32:51 PM Eastern Time --> |
<!-- Copyright (c) 2020 Donnelley Financial Solutions, Inc. All Rights Reserved. --> |
<xsd:schema xmlns:nonnum="http://www.xbrl.org/dtr/type/non-numeric" xmlns:num="http://www.xbrl.org/dtr/type/numeric" xmlns:us-types="http://fasb.org/us-types/2019-01-31" xmlns:altr="http://www.altair.com/20200914" xmlns:dei="http://xbrl.sec.gov/dei/2019-01-31" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:sic="http://xbrl.sec.gov/sic/2011-01-31" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.altair.com/20200914" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> |
| <xsd:import schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" namespace="http://www.xbrl.org/2003/instance"/> |
| <xsd:import schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" namespace="http://www.xbrl.org/2003/linkbase"/> |
| <xsd:import schemaLocation="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd" namespace="http://xbrl.sec.gov/dei/2019-01-31"/> |
| <xsd:import schemaLocation="http://www.xbrl.org/dtr/type/numeric-2009-12-16.xsd" namespace="http://www.xbrl.org/dtr/type/numeric"/> |
| <xsd:import schemaLocation="http://www.xbrl.org/dtr/type/nonNumeric-2009-12-16.xsd" namespace="http://www.xbrl.org/dtr/type/non-numeric"/> |
| <xsd:import schemaLocation="http://xbrl.sec.gov/sic/2011/sic-2011-01-31.xsd" namespace="http://xbrl.sec.gov/sic/2011-01-31"/> |
| <xsd:import schemaLocation="https://xbrl.sec.gov/naics/2017/naics-2017-01-31.xsd" namespace="http://xbrl.sec.gov/naics/2017-01-31"/> |
| <xsd:import schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" namespace="http://xbrl.org/2005/xbrldt"/> |
| <xsd:annotation> |
| | <xsd:appinfo> |
| | | <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="altr-20200914_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:title="Label Links, all" xlink:type="simple"/> |
| | | <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="altr-20200914_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:title="Presentation Links, all" xlink:type="simple"/> |
| | | <link:roleType roleURI="http://www.altair.com//20200914/taxonomy/role/DocumentDocumentAndEntityInformation" id="Role_DocumentDocumentAndEntityInformation"> |
| <link:definition> 100000 - Document - Document and Entity Information </link:definition> |
| <link:usedOn> link:calculationLink </link:usedOn> |
| <link:usedOn> link:presentationLink </link:usedOn> |
| <link:usedOn> link:definitionLink </link:usedOn> |
| </link:roleType> |
| | | </xsd:appinfo> |
| | </xsd:annotation> |
| </xsd:schema> |