Note 4. Revenue

Revenue from sales of our products and services is recognized either at the point in time when control of the products is transferred to our customers or over time as services are provided in an amount that reflects the consideration we expect to be entitled to in exchange for the products or services. See Note 2. Summary of Significant Accounting Pronouncements for additional information related to our revenue recognition policies and Note 6. Segment Reporting for a description of each segment's product and service offerings.

Disaggregation of Revenue

The following table disaggregates the revenue associated with our major product and service offerings:



	13 weeks ended						39 weeks ended
	January 25, 2020			January 26, 2019			January 25, 2020			January 26, 2019
Retail
Product Sales	$	400,170		$	431,555		$	1,320,587		$	1,396,940
Rental Income	48,614			56,019			119,729			134,251
Service and Other Revenue ^(a)	9,204			10,572			34,097			37,946
Retail Total Sales	$	457,988		$	498,146		$	1,474,413		$	1,569,137
Wholesale Sales	$	66,996		$	78,508		$	179,515		$	209,282
DSS Sales ^(b)	$	6,435		$	5,237		$	17,024		$	15,848
Eliminations ^(c)	$	(29,127	)	$	(33,883	)	$	(76,775	)	$	(94,009	)
Total Sales	$	502,292		$	548,008		$	1,594,177		$	1,700,258


(a)	Service and other revenue primarily relates to brand partnerships and other service revenues.


(b)	DSS sales primarily relate to direct-to-student subscription-based revenue.


(c)	The sales eliminations represent the elimination of Wholesale sales and fulfillment service fees to Retail and the elimination of Retail commissions earned from Wholesale.

Contract Assets and Contract Liabilities

Contract assets represent the sale of goods or services to a customer before we have the right to obtain consideration from the customer. Contract assets consist of unbilled amounts at the reporting date and are transferred to accounts receivable when the rights become unconditional. Contract assets (unbilled receivables) were $0 as of January 25, 2020, January 26, 2019 and April 27, 2019 on our condensed consolidated balance sheets.

Contract liabilities represent an obligation to transfer goods or services to a customer for which we have received consideration and consists of our deferred revenue liability (deferred revenue). Deferred revenue primarily consists of advanced payments from customers related to textbook rental and subscription-based performance obligations that have not yet been satisfied, as well as unsatisfied performance obligations associated with partnership marketing services. Deferred revenue is recognized ratably over the terms of the related rental or subscription periods, or when the contracted services are provided to our partnership marketing customers. Deferred revenue of $60,708, $69,662, and $20,418 is recorded within Accrued Liabilities on our condensed consolidated balance sheets for the periods ended January 25, 2020, January 26, 2019 and April 27, 2019, respectively. The following table presents changes in contract liabilities:



	39 weeks ended
	January 25, 2020			January 26, 2019
Deferred revenue at the beginning of period	$	20,418		$	20,144
Additions to deferred revenue during the period	170,375			189,832
Reductions to deferred revenue for revenue recognized during the period	(130,085		)	(140,314		)
Deferred revenue balance at the end of period	$	60,708		$	69,662

As of January 26, 2019, we expect to recognize $60,708 of the deferred revenue balance within the next 12 months.