Years Ended December 31,
Years Ended December 31,
Years Ended December 31,
2019
2018
2017
Revenues
ACI On Premise
$579,334
$576,755
$598,590
ACI On Demand
678,960
433,025
425,601
Total revenue
$1,258,294
$1,009,780
$1,024,191
Segment Adjusted EBITDA
ACI On Premise
$ 321,305
$ 323,902
$ 347,094
ACI On Demand
66,501
12,015
(1,832 )
Depreciation and amortization
(122,569 )
(97,350 )
(102,224 )
Stock-based compensation expense
(36,763 )
(20,360 )
(13,683 )
Corporate and unallocated expenses
(104,718 )
(92,296 )
(144,715 )
Interest, net
(52,066 )
(30,388 )
(38,449 )
Other, net
520
(3,724 )
(2,619 )
Income before income taxes
$ 72,210
$ 91,799
$ 43,572
Depreciation and amortization
ACI On Premise
$ 11,992
$ 11,634
$ 13,094
ACI On Demand
34,395
31,541
34,171
Corporate
76,182
54,175
54,959
Total depreciation and amortization
$ 122,569
$ 97,350
$ 102,224
Stock-based compensation expense
ACI On Premise
$ 7,651
$ 4,348
$ 2,234
ACI On Demand
7,995
4,338
2,230
Corporate
21,117
11,674
9,219
Total stock-based compensation expense
$36,763
$20,360
$13,683
10 .
segment information .
the company reports financial performance based on its segments aci on premise and aci on demand and analyzes segment adjusted ebitda as a measure of segment profitability .
the company ’ s interim chief executive officer is also the chief operating decision maker - " codm " .
the codm together with other senior management personnel focus their review on consolidated financial information and the allocation of resources based on operating results including revenues and segment adjusted ebitda for each segment separate from corporate operations .
aci on premise serves customers who manage their software on site or through a third-party cloud service provider .
these onpremise customers use the company ’ s software to develop sophisticated solutions which are often part of a larger system located and managed at the customer specified site .
these customers require a level of control and flexibility that aci on premise solutions can offer and they have the resources and expertise to take a lead role in managing these solutions .
aci on demand serves the needs of banks merchants and billers who use payments to facilitate their core business .
these ondemand solutions are maintained and delivered through the cloud via our global data centers and are available in either a singletenant environment for saas offerings or in a multi-tenant environment for paas offerings .
revenue is attributed to the reportable segments based upon the product sold and mechanism for delivery to the customer .
expenses are attributed to the reportable segments in one of three methods -1 direct costs of the segment -2 labor costs that can be attributed based upon time tracking for individual products or -3 costs that are allocated .
allocated costs are generally marketing and sales related activities as well as information technology and facilities related expense for which multiple segments benefit .
the company also allocates certain depreciation costs to the segments .
segment adjusted ebitda is the measure reported to the codm for purposes of making decisions on allocating resources and assessing the performance of the company ’ s segments and therefore segment adjusted ebitda is presented in conformity with asc 280 segment reporting .
segment adjusted ebitda is defined as earnings -loss from operations before interest income tax expense -benefit depreciation and amortization - “ ebitda ” adjusted to exclude stock-based compensation and net other income -expense .
corporate and unallocated expenses consist of the corporate overhead costs that are not allocated to reportable segments .
these overhead costs relate to human resources finance legal accounting merger and acquisition activity and other costs that are not considered when management evaluates segment performance .
for the year ended december 31 2017 corporate and unallocated expenses included $ 46 .
7 million of general and administrative expense for the legal judgment discussed in note 15 commitments and contingencies .
the following is selected financial data for the company ’ s reportable segments for the periods indicated -in thousands : .
assets are not allocated to segments and the company ’ s codm does not evaluate operating segments using discrete asset information .

Question: Which group of people does ACI on Premise serve?
Answer: customers who manage their software on site or through a third-party cloud service provider.