Each business day, TheStreet.com Ratings updates its ratings on the stocks it covers. The proprietary ratings model projects a stock's total return potential over a 12-month period, including both price appreciation and dividends. Buy, hold or sell ratings designate how the Ratings group expects these stocks to perform against a general benchmark of the equities market and interest rates. While the ratings model is quantitative, it uses both subjective and objective elements. For instance, subjective elements include expected equities market returns, future interest rates, implied industry outlook and company earnings forecasts. Objective elements include volatility of past operating revenue, financial strength and company cash flows. However, the rating does not incorporate all of the factors that can alter a stock's performance. For example, it doesn't always factor in recent corporate or industry events that could affect the stock price, nor does it include recent technology developments and competitive dynamics that may affect the company. For those reasons, we believe a rating alone cannot tell the whole story, and that it should be part of an investor's overall research. The following ratings changes were generated on April 30. Xilinx ( XLNX), which designs programmable logic solutions, has been upgraded to buy. For the fourth quarter, revenue increased 7.3% year over year to $475.8 million, and earnings per share improved 26% year over year to 36 cents. This year, the market expects an improvement in full-year EPS to $1.47 from $1.27 for 2007. The company's debt-to-equity ratio of 0.60 is higher than that of the industry average, but its company quick ratio of 4.54 is very high and demonstrates very strong liquidity. Return on equity has improved slightly year over year to 22%. Xilinx had been rated hold since Nov. 23.