Obviousness

The obviousness of US patent 7161506 under 35 U.S.C. § 103 can be analyzed by combining the teachings of U.S. Pat. No. 5,467,087 to Chu ("Chu") with general knowledge prevalent in the art, as described within the background section of US7161506 itself. A person having ordinary skill in the art (PHOSITA) would have been motivated to combine these references to overcome the explicit limitations of prior art content-dependent compression systems.

Key Combination of Prior Art References:

1. U.S. Pat. No. 5,467,087 to Chu (referenced as "Chu" in US7161506).
2. General knowledge of the problems in data compression, including:
   • The difficulty in unambiguously identifying various data types, especially when interspersed or partially compressed. [cite: Background]
   • The "natural variation" problem, where a single lossless compression technique yields significant variations in compression ratio for different data content and sizes. [cite: Background]
   • The "negative compression" problem, where certain compression techniques expand, rather than compress, highly compressed or random data. [cite: Background]
   • The difficulty in predicting which data encoding technique yields the highest compression ratio even for a known data type. [cite: Background]

Analysis of Obviousness:

The primary claims of US7161506, as outlined in its "Summary of the Invention" and "Description" sections, center on a hybrid data compression approach utilizing both content-dependent and content-independent methods, particularly with fallback mechanisms and comparison of multiple encoding results against thresholds.

1. Combining Content-Dependent and Content-Independent Compression Paths (Claim 1, broadly):

• Chu's Teaching: Chu discloses a data compression system that includes a "data pre-compressor" to identify the data type of an input stream and a "data compressor" that selects a compression method from a preselected set "to compress the input data stream, with the intention of producing the best available compression ratio for that particular data type." [cite: Background] This describes a content-dependent approach.
• US7161506's Claim: US7161506 claims a method that includes "performing content dependent data compression on the data block, if the data type of the data block is identified; [and] performing content independent data compression on the data block, if the data type of the data block is not identified." [cite: Summary of the Invention]
• Motivation to Combine: The background of US7161506 explicitly states a "fundamental limitation" with Chu's content-dependent technique: "the need to unambiguously identify various data types." It further notes that "data types may be interspersed or partially compressed, making data type recognition difficult and/or impractical." [cite: Background]
  A PHOSITA, faced with these known limitations of Chu's system (i.e., its inability to process data whose type cannot be identified), would be motivated to provide a robust solution. The obvious engineering solution would be to implement a fallback or alternative path for such unidentifiable data. A "content independent" approach, where a variety of general-purpose encoders are tried without specific data type knowledge, is a logical and common strategy to attempt compression when type-specific methods are not applicable. This combination would ensure that data blocks, regardless of whether their type can be identified by Chu's pre-processor, are still subjected to compression attempts, thus improving the overall utility and efficiency of the system.

2. Evaluating Multiple Encoders, Compression Ratios, and Thresholds (Claims detailing content-independent and content-dependent compression):

• Chu's Teaching: Chu's system selects "a data compression method from a preselected set of methods... with the intention of producing the best available compression ratio." [cite: Background] While aiming for the "best," Chu does not explicitly detail a mechanism for how this best ratio is determined or what happens if no effective compression is achieved.
• US7161506's Claim: US7161506 claims steps such as "encoding the data block with a plurality of encoders to provide a plurality of encoded data blocks; determining a compression ratio obtained for each of the encoders; comparing each of the determined compression ratios with a first compression threshold; selecting for output the input data block and appending a null compression descriptor... if all of the encoder compression ratios do not meet the first compression threshold; and selecting for output the encoded data block having the highest compression ratio... if at least one of the compression ratios meet the first compression threshold." [cite: Summary of the Invention] Similar steps are claimed for content-dependent compression with a "second compression threshold." [cite: Summary of the Invention]
• Motivation to Combine: The background of US7161506 highlights "significant variations in the compression ratio obtained when using a single lossless data compression technique" ("natural variation") and the risk of "negative compression" (data expansion). [cite: Background]
  A PHOSITA, aiming to truly achieve "the best available compression ratio" as intended by Chu, and to mitigate the known problems of natural variation and negative compression, would find it obvious to implement a concrete evaluation mechanism. This involves systematically:
  1. Trying multiple available encoders on a data block (a "plurality of encoders").
  2. Measuring the actual compression performance of each (determining a compression ratio).
  3. Setting a minimum "compression threshold" to avoid ineffective compression or, worse, data expansion.
  4. Selecting the best-performing algorithm that meets the threshold.
  5. As a failsafe, outputting the original, uncompressed data with a "null compression descriptor" if no encoder achieves the minimum threshold, thereby preventing unwanted data expansion. This is a common-sense engineering approach to optimize performance and prevent detrimental outcomes, well within the grasp of a PHOSITA.

3. Fallback from Content-Dependent to Content-Independent Compression (Alternative Method Claim):

• Chu's Teaching: Chu provides a content-dependent selection.
• US7161506's Claim: US7161506 claims an alternative method including "performing content independent data compression on the data block, if the data type of the data block is not identified or if the compression ratio of the compressed data block obtained using the content dependent compression does not meet the first compression threshold." [cite: Summary of the Invention]
• Motivation to Combine: As articulated in US7161506's background, "given a known data type... it may be difficult and/or impractical to predict which data encoding technique yields the highest compression ratio." [cite: Background] This means that even if Chu's system correctly identifies a data type and selects a content-dependent algorithm, that algorithm might still perform poorly (e.g., fail to meet a compression threshold).
  A PHOSITA, recognizing this unpredictability and the desire to maximize compression, would be motivated to introduce a robust fallback. If the primary content-dependent compression attempt (based on Chu's mechanism) proves ineffective (i.e., its compression ratio doesn't meet a specified threshold), then attempting a content-independent strategy (trying a broader range of general-purpose encoders) as a secondary measure is an obvious engineering refinement. This ensures that the system doesn't prematurely settle for poor compression or no compression if a more effective method could be found through a less specific approach.

In summary, the advancements claimed in US7161506, particularly the integration of content-independent compression as a primary or fallback option, and the detailed mechanism for evaluating multiple compression results against thresholds, represent obvious solutions to well-known problems explicitly discussed in the patent's own background section. A PHOSITA, armed with Chu's content-dependent framework and an understanding of its limitations and common compression challenges, would have been motivated to combine these elements to create a more robust and effective data compression system.