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 segments product and service offerings.

Disaggregation of Revenue

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



	13 weeks ended
	July 27, 2019			July 28, 2018
Retail
Product Sales	$	246,375		$	256,111
Rental Income	17,430			19,639
Service and Other Revenue ^(a)	10,851			11,335
Retail Total Sales	$	274,656		$	287,085
Wholesale Sales	$	72,309		$	89,944
DSS Sales ^(b)	$	5,374		$	5,677
Eliminations ^(c)	$	(32,682	)	$	(45,222	)
Total Sales	$	319,657		$	337,484


(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 July 27, 2019, July 28, 2018 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 $14,188, $15,851, and $20,418 is recorded within Accrued Liabilities on our condensed consolidated balance sheets for the periods ended July 27, 2019, July 28, 2018 and April 27, 2019, respectively.

The following table presents changes in contract liabilities during the 13 weeks ended July 27, 2019:



	13 weeks ended
	July 27, 2019			July 28, 2018
Deferred revenue at the beginning of period	$	20,418		$	20,144
Additions to deferred revenue during the period	18,083			25,100
Reductions to deferred revenue for revenue recognized during the period	(24,313		)	(29,393		)
Deferred revenue balance at the end of period	$	14,188		$	15,851

As of July 27, 2019, we expect to recognize $14,188 of the deferred revenue balance within in the next 12 months.