Patent Publication Number: US-10318202-B2

Title: Non-volatile memory apparatus and data deduplication method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of U.S. provisional application Ser. No. 62/474,023, filed on Mar. 20, 2017. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a memory apparatus, and more particularly, relates to a non-volatile memory apparatus and a data de-duplication method thereof. 
     2. Description of Related Art 
     In comparison with traditional hard disk drives, flash memory storage equipments have favorable reading/writing performance and low power consumption, and this is why the flash memories are widely applied in data storage systems. In certain storage applications, the same data may have multiple duplications in the storage equipment, and these duplications will increase a data written count. How to reduce the amount of writes while improving write performance as well as endurance is one important issue that needs to be addressed. 
     The existing approach can perform a compression for the data and then writes the compressed data into the flash memory. This data compression technique can reduce a data volume of duplicated data so as to reduce the amount of writes. In any case, the data volume that the data compression technique can reduce depends on data patterns. In certain applications, the data cannot be compressed at all. In other applications, the data can be well compressed. Consequently, because the data patterns are not exactly the same in terms of compressibility, the length of each data after compression may have a different change. If the each of the compressed data has a different length, the data compression may consume a lot of overload of FTL (Flash Translation Layer) just for managing the compressed data. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a non-volatile memory apparatus and a data de-duplication method thereof, which are capable of reducing the number of times that the same encoded data is repeatedly written into the non-volatile memory. 
     A non-volatile memory apparatus is provided according to the embodiments of the invention. The non-volatile memory apparatus includes a non-volatile memory and a controller. The controller is coupled to the non-volatile memory. The controller is configured to perform an error checking and correcting (ECC) method to convert a raw data into an encoded data. The controller is configured to perform the data de-duplication method to reduce a number of times that the same encoded data is repeatedly written to the non-volatile memory. The data de-duplication method includes: generating a feature information corresponding to the raw data by reusing the ECC method; looking up a feature list using the feature information; not writing the encoded data corresponding to the raw data into the non-volatile memory when the feature information is found in the feature list; and adding the feature information corresponding to the raw data into the feature list and writing the encoded data corresponding to the raw data into the non-volatile memory when the feature information is not found in the feature list. 
     A data de-duplication method of a non-volatile memory apparatus is provided according to the embodiments of the invention, which is used to reduce the number of times that the same encoded data is repeatedly written into the non-volatile memory. The non-volatile memory apparatus is configured to perform an ECC method so as to convert a raw data into an encoded data. The data de-duplication method includes: generating a feature information corresponding to the raw data by reusing the ECC method; looking up a feature list using the feature information; not writing the encoded data corresponding to the raw data into the non-volatile memory when the feature information is found in the feature list; and adding the feature information corresponding to the raw data into the feature list and writing the encoded data corresponding to the raw data into the non-volatile memory when the feature information is not found in the feature list. 
     Based on the above, the non-volatile memory apparatus and the data de-duplication method thereof described in the embodiments of the invention can generate the feature information corresponding to the raw data by reusing the existing ECC method. Upon comparing the feature information with feature list, it can be learnt about whether the encoded data corresponding to the raw data has been written into the non-volatile memory. As a result, the non-volatile memory apparatus and the data de-duplication method thereof described in the embodiments of the invention are capable of reducing the number of times that the same encoded data is repeatedly written into the non-volatile memory. 
     To make the above features and advantages of the disclosure more comprehensible, several embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a circuit block diagram illustrating a non-volatile memory apparatus according to an embodiment of the invention. 
         FIG. 2  is a schematic flowchart illustrating a data de-duplication method according to an embodiment of the invention. 
         FIG. 3  is a schematic flowchart illustrating a data de-duplication method according to another embodiment of the invention. 
         FIG. 4  is a circuit block diagram illustrating the controller depicted in  FIG. 1  according to an embodiment of the invention. 
         FIG. 5  is a circuit block diagram illustrating the controller depicted in  FIG. 1  according to another embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     The term “coupled (or connected)” used in this specification (including claims) may refer to any direct or indirect connection means. For example, “a first device is coupled (connected) to a second device” should be interpreted as “the first device is directly connected to the second device” or “the first device is indirectly connected to the second device through other devices or connection means”. Moreover, elements/components/steps with same reference numerals represent same or similar parts in the drawings and embodiments. Elements/components/steps with the same reference numerals or names in different embodiments may be cross-referenced. 
       FIG. 1  is a circuit block diagram illustrating a non-volatile memory apparatus  100  according to an embodiment of the invention. Based on design requirements, the non-volatile memory apparatus  100  may be a USB drive, a SSD (solid state disc) or other storage devices. The non-volatile memory apparatus  100  may be coupled to a host  10 . The host  10  may be a computer, a handheld phone, a multimedia player, a camera or other electronic devices. When the host  10  sends a write command to the non-volatile memory apparatus  100 , the non-volatile memory apparatus  100  can write a data of the host  10  into a non-volatile memory in the non-volatile memory apparatus  100  according to addressing of the write command. When the host  10  sends a read command to the non-volatile memory apparatus  100 , the non-volatile memory apparatus  100  can return the corresponding data to the host  10  according to addressing of the read command. 
     In the embodiment shown by  FIG. 1 , the non-volatile memory apparatus  100  includes a non-volatile memory  110  and a controller  120 . Based on design requirements, the non-volatile memory  110  may be an NAND flash memory or other non-volatile memory circuits/devices. The controller  120  is coupled to the non-volatile memory  110 . When the host  10  sends one write command, the controller  120  can perform an error checking and correcting (a.k.a. ECC) method to convert a raw data of the host  10  into an encoded data (or known as a codeword). Based on design requirements, the ECC method may be a BCH (Bose-Chaudhuri-Hocquengh) algorithm, a LDPC (Low Density Parity Check) algorithm, or other ECC algorithms. The BCH algorithm and the LDPC algorithm belong to the prior art, and thus description regarding the same is not repeated hereinafter. The controller  120  can address the non-volatile memory  110  according to logical addresses of the write command, so as to write the encoded data into the non-volatile memory  110 . 
     The followings take the LDPC algorithm as an example. The controller  120  can perform the LDPC algorithm to convert the raw data of the host  10  into a plurality of parity bits. The raw data and the parity bits are used together as the codeword (the encoded data). According to the logical addresses of the write command, the controller  120  can address the non-volatile memory  110  and writes the codeword (the encoded data) into the non-volatile memory  110 . Implementation regarding other ECC algorithms (e.g., the BCH algorithm) may be deduced with reference to the related description of the LDPC algorithm, which is not repeated hereinafter. 
     After one read command is sent by the host  10 , the controller  120  can address the non-volatile memory  110  according to the logical addresses of the read command, so as to read one corresponding encoded data from the non-volatile memory  110 . The controller  120  can perform the ECC method for the encoded data, so as to obtain a decoded data (the raw data). The ECC method can correct errors occurred during the transmission process. 
     The followings take the LDPC algorithm as an example. After one LDPC decoding is complete, the controller  120  can obtain one decoded codeword v. The controller  120  can perform a syndrome operation to check the decoded codeword v by using Equation 1 below, so as to obtain a syndrome [c 0  c 1  . . . c m-1 ]. H in Equation 1 is a parity check matrix having a property of sparse matrix. Elements in the parity check matrix H are 1 or 0, and the number of the elements being 1 is far less than the number of the elements being 0. The parity check matrix H belongs to the prior art, which is not described hereinafter. If the syndrome [c 0  c 1  . . . c m-1 ] is not a 0 vector (0 matrix, i.e., all the elements c 0  to c m-1  are 0), the controller  120  can perform an iterative operation (perform the LDPC decoding once again) on the decoded codeword v, so as to obtain a new decoded codeword v. The controller  120  can check the new decoded codeword v using Equation 1 again to obtain a new syndrome [c 0  c 1  . . . c m-1 ]. In this way, the iterative operation will be performed multiple times until the syndrome [c 0  c 1  . . . c m-1 ] is the 0 vector (0 matrix) so that the iterative operation can be terminated (i.e., the LDPC decoding on the decoded codeword is successful). When the LDPC decoding on the decoded codeword is successful, the controller  120  can return the decoded data (the decoded codeword v) to the host  10 . 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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       FIG. 2  is a schematic flowchart illustrating a data de-duplication method according to an embodiment of the invention. With reference to  FIG. 1  and  FIG. 2 , the controller  120  can perform the data de-duplication method to reduce a number of times that the same encoded data is repeatedly written to the non-volatile memory  110 . In step S 210 , the controller  120  can generate a feature information corresponding to the raw data of the host  10  by reusing the ECC method. Any calculating operation and/or any calculating result of the ECC method can be reused to generate the feature information in step S 210 . 
     Part or all of the parity bits generated by reusing the ECC method can be used as the feature information in step S 210 . For instance, it is assumed that a data volume of the raw data is 4 KB. If the data volume processed by the ECC method each time is 1 KB, the raw data may be divided into 4 parts D 1 , D 2 , D 3  and D 4 , and a data volume of each part is 1 KB. The ECC method can perform an ECC calculation for the part D 1  to obtain one set of parity bits P 1 . By analogy, the ECC method can perform the ECC calculation for the other parts D 2 , D 3  and D 4  to obtain three sets of parity bits P 2 , P 3  and P 4 . Based on design requirements, in some embodiments, all of the parity bits P 1 , P 2 , P 3  and P 4  can be reused as the feature information of the raw data in step S 210 . 
     In some other embodiments, part of the parity bits P 1 , P 2 , P 3  and P 4  can be reused as the feature information of the raw data in step S 210 . For example, a first half (or a second half) of P 1 , a first half (or a second half) of P 2 , a first half (or a second half) of P 3  and a first half (or a second half) of P 4  can be taken as the feature information of the raw data in step S 210 . As another example, contents at odd positions (or even positions) of P 1 , contents at odd positions (or even positions) of P 2 , contents at odd positions (or even positions) of P 3  and contents at odd positions (or even positions) of P 4  can be taken as the feature information of the raw data in step S 210 . 
     In still some other embodiments, the feature information of the raw data may be generated by performing a logic operation using part or all of parity bits of the encoded data corresponding to the raw data in step S 210 . For instance, assuming that the data volume of the raw data is 4 KB and the data volume processed by the ECC method each time is 1 KB, the raw data may be divided into 4 parts D 1 , D 2 , D 3  and D 4 . The ECC method can perform the ECC calculation for each of the 4 parts D 1 , D 2 , D 3  and D 4  to obtain four sets of parity bits P 1 , P 2 , P 3  and P 4 . The feature information of the raw data may be generated by performing an exclusive OR (XOR) operation using P 1 , P 2 , P 3  and P 4  in step S 210 . Given that the data volume of the raw data is 4 KB and the data volume processed by the ECC method each time is 4 KB, the ECC method can perform the ECC calculation for the raw data to obtain one set of parity bits P. This set of parity bits P may be divided into n parts (n may be decided based on design requirements). For example, P is divided into four sets of parity bits P 5 , P 6 , P 7  and P 8 . The feature information of the raw data may be generated by performing the logic operation (e.g., the XOR operation) using P 5 , P 6 , P 7  and P 8  in step S 210 . 
     In yet some other embodiments, one or more syndromes of the raw data may be generated by performing a syndrome operation of the ECC method for the raw data in step S 210 . For instance, in the example of the LDPC algorithm, the syndrome operation may be LDPC syndrome operation in Equation 1 above, but the decoded codeword v in Equation 1 is replaced by the raw data. That is to say, the syndrome of the raw data is obtained by multiplying the raw data by H T . 
     Part or all of bits of the syndromes of the raw data can be used as the feature information in step S 210 . For instance, assuming that the data volume of the raw data is 4 KB and the data volume processed by the ECC method each time is 1 KB, the raw data may be divided into 4 parts D 1 , D 2 , D 3  and D 4 . A syndrome S 1  of D 1  may be generated by performing the syndrome operation of the ECC method for the part D 1  in step S 210 . For instance, in the example of the LDPC algorithm, the syndrome operation may be S 1 =D 1 *H T  (see Equation 1 above for more details) and by which the syndrome S 1  of D 1  may be obtained. By analogy, three syndromes S 2 , S 3  and S 4  may be generated by respectively performing the syndrome operation of the ECC method for the other parts D 2 , D 3  and D 4  in step S 210 . Based on design requirements, in some embodiments, all of bits of the syndromes S 1 , S 2 , S 3  and S 4  can be used as the feature information of the raw data in step S 210 . 
     In some other embodiments, part of bits of the syndromes S 1 , S 2 , S 3  and S 4  can be used as the feature information of the raw data in step S 210 . For example, a first half (or a second half) of S 1 , a first half (or a second half) of S 2 , a first half (or a second half) of S 3  and a first half (or a second half) of S 4  can be taken as the feature information of the raw data in step S 210 . As another example, contents at odd positions (or even positions) of S 1 , contents at odd positions (or even positions) of S 2 , contents at odd positions (or even positions) of S 3  and contents at odd positions (or even positions) of S 4  can be taken as the feature information of the raw data in step S 210 . 
     In still some other embodiments, the feature information of the raw data may be generated by performing the logic operation using part or all of bits of the syndromes of the raw data in step S 210 . For instance, assuming that the data volume of the raw data is 4 KB and the data volume processed by the ECC method each time is 1 KB, the raw data may be divided into 4 parts D 1 , D 2 , D 3  and D 4 . The ECC method can perform the syndrome operation for each of the 4 parts D 1 , D 2 , D 3  and D 4  to obtain four syndromes S 1 , S 2 , S 3  and S 4 . The feature information of the raw data may be generated by performing the XOR operation using S 1 , S 2 , S 3  and S 4  in step S 210 . Given that the data volume of the raw data is 4 KB and the data volume processed by the ECC method each time is 4 KB, the ECC method can perform the syndrome operation for the raw data to obtain one syndrome S. This syndrome S may be divided into n parts (n may be decided based on design requirements). For example, S may be divided into four syndromes S 5 , S 6 , S 7  and S 8 . The feature information of the raw data may be generated by performing the logic operation (e.g., the XOR operation) using S 5 , S 6 , S 7  and S 8  in step S 210 . 
     With reference to  FIG. 2 , in step S 220 , the controller  120  can look up the feature list using the feature information of step S 210 . A data structure of the feature list is not particularly limited by the present embodiment. Based on design requirements, in some embodiments, the data structure of the feature list is a data link or other structures. Each record in the feature list contains a feature field. When the feature information of the raw data is found in the feature list by the controller  120 , the controller  120  does not write the encoded data corresponding to the raw data into the non-volatile memory  110  (step S 230 ). When the feature information of the raw data is not found in the feature list by the controller  120 , the controller  120  adds the feature information of the raw data into the feature list (step S 240 ) and the controller  120  writes the encoded data corresponding to the raw data into the non-volatile memory  110  (step S 250 ). 
       FIG. 3  is a schematic flowchart illustrating a data de-duplication method according to another embodiment of the invention. Steps S 210  and S 220  shown in  FIG. 3  can refer to the related description of  FIG. 2 , which is not repeated hereinafter. Based on design requirements, in some embodiments, the data structure of the feature list is a data link or other structures. Each record in the feature list contains a feature field and a physical address field. With reference to  FIG. 1  and  FIG. 3 , when it is determined in step S 220  that the feature information of the raw information can be found by the controller  120 , the controller  120  will perform step S 330 . When it is determined in step S 220  that the feature information of the raw data cannot be found by the controller  120 , the controller  120  will perform step S 350 . 
     In step S 330 , the controller  120  can move one record having the feature information in the feature list to a first-end position of the feature list (e.g., moving to a head position of the feature list). In some other embodiments, the controller  120  can move one corresponding record matching the feature information in the feature list to a tail position of the feature list. In step S 340 , the controller  120  can update an address mapping table (which will be described in detail later) but does not write the corresponding encoded data into the non-volatile memory  110 . 
     In step S 350 , the controller  120  can add the feature information to the first-end position of the feature list (e.g., adding to the head position of the feature list). In some application scenarios, a capacity of the feature list is limited. When the feature information is to be added to the first-end position (e.g., the head position) of the feature list but the feature list is already full, the controller  120  can discard a content at the second-end position of the feature list (e.g., discarding a content at the tail position of the feature list). In some other embodiments, the controller  120  can add the new feature information to the tail position of the feature list and discard a content at the head position of the feature list. In step S 360 , the controller  120  can update the address mapping table (which will be described in detail later). In step S 370 , the controller  120  can write the encoded data corresponding to the raw data into the non-volatile memory  110 . 
     For instance, it is assumed herein that the host  10  sends one write command (a first write command) for writing the raw data into a logical address LADD 1  in a previous time, and then sends another write command (a second write command) for writing the same raw data into a logical address LADD 2  in a current time. It assumed that the logical address LADD 1  corresponds to a physical address PADD 1  and the logical address LADD 2  corresponds to a physical address PADD 2 . In said previous time, a raw data of the first write command is converted into a feature information CH 1  in step S 210 , and it is determined in step S 220  that the feature list does not include a related record of the feature information CH 1 . Accordingly, the controller  120  adds a correspondence relation between the feature information CH 1  and the physical address PADD 1  into the feature list (step S 350 ), the controller  120  adds a correspondence relation between the logical address LADD 1  and the physical address PADD 1  to the address mapping table (step S 360 ), and the controller  120  writes the encoded data corresponding to the raw data into the non-volatile memory  110  at the physical address PADD 1 . In said current time, a raw data of the second write command is converted into the feature information CH 1  in step S 210 , and it is determined in step S 220  that the feature list includes the related record of the feature information CH 1 . In other words, the feature list records that the encoded data corresponding to the feature information CH 1  has been written into the physical address PADD 1 . Accordingly, the controller  120  moves this record including the feature information CH 1  in the feature list to the first-end position of the feature list (step S 330 ), and the controller  120  adds a correspondence relation between the logical address LADD 2  and the physical address PADD 1  to the address mapping table (step S 340 ). However, the controller  120  does not write the encoded data corresponding to the same raw data of the second write command into the non-volatile memory  110  at the physical address PADD 2 . By doing so, the controller  120  can reduce the number of times that the same encoded data is repeatedly written into the non-volatile memory  110 . 
     It should be noted that, under different application scenarios, related functions of the non-volatile memory  110  and/or the controller  120  may be implemented in form of software, firmware or hardware by utilizing common programming languages (e.g., C or C++), hardware description languages (e.g., Verilog HDL or VHDL) or other suitable programming languages. The programming language capable of executing the related functions can be arranged into any known computer-accessible media such as magnetic tapes, semiconductor memories, magnetic disks or compact disks (e.g., CD-ROM or DVD-ROM); or the programming language may be transmitted via the Internet, a wired communication, a wireless communication or other communication mediums. Said programming language may be stored in the computer-accessible media, so that a computer processor can access/execute programming codes of the software (or the firmware). As for hardware implementation, in combination with the aspect disclosed by the embodiments of the invention, various logical blocks, modules and circuit used in one or more controllers, a microcontroller, an application-specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array (FPGA) and/or other processing units may be utilized to realize or execute the function described in the invention. In addition, the apparatus and the method of the invention can also be implemented by a combination of software and hardware. 
       FIG. 4  is a circuit block diagram illustrating the controller  120  depicted in  FIG. 1  according to an embodiment of the invention. In the embodiment shown by  FIG. 4 , the controller  120  includes a central processing unit  121 , a memory control circuit  122 , a memory buffer  123 , a de-duplication circuit  124  and an error checking and correcting (a.k.a. ECC) circuit  125 . The central processing unit  121  and the memory buffer  123  are coupled to the host  10  via a communication interface. Based on design requirements, said communication interfaces include SCSI (small computer system interface), SAS (Serial Attached SCSI) interface, ESDI (Enhanced Small Disk Interface), SATA (serial advanced technology attachment) interface, PCI-express (peripheral component interconnect express) interface, IDE (integrated drive electronics) interface, USB (universal serial bus) interface, Thunderbolt interface or other interfaces. An interface structure between the host  10  and the non-volatile memory apparatus  100  is not particularly limited by the present embodiment. 
     When the host  10  sends the write command, the raw data to be written may be temporarily stored in the memory buffer  123 , and the central processing unit  121  can convert/decode the write command (containing the logical addresses) of the host  10  into a corresponding internal control signal (containing the physical addresses of the non-volatile memory  110 ) and provides the internal control signal to the memory control circuit  122  and/or the memory buffer  123 . An example of the memory buffer  123  includes a DRAM dynamic random access memory), a SRAM (static random access memory or other volatile memories. The ECC circuit  125  is coupled to the memory buffer  123  for receiving the raw data. The ECC circuit  125  can execute the ECC method (algorithm) to encode the raw data temporarily stored in the memory buffer  123  into the codeword (i.e., the encoded data). In some embodiments, the ECC circuit  125  can execute the BCH algorithm, the LDPC algorithm or other ECC algorithms. 
     The ECC circuit  125  can generate the feature information of the raw data to be written by reusing the ECC method, and stores the feature information into the memory buffer  123 . The de-duplication circuit  124  receives the feature information generated by the ECC circuit  125  via the memory buffer  123 . The de-duplication circuit  124  looks up the feature list using the feature information so as to obtain a look-up result. The central processing unit  121  is coupled to the de-duplication circuit  124  for receiving the look-up result. When the feature information is found in the feature list, the central processing unit  121  does not write the encoded data into the non-volatile memory  110 . When the feature information is not found in the feature list, the central processing unit  121  sends the internal control signal to the memory control circuit  122  and the de-duplication circuit  124 . According to the internal control signal, the memory control circuit  122  can address/control the non-volatile memory  110 , so as to write the encoded data into the non-volatile memory  110 . According to the internal control signal, the de-duplication circuit  124  adds the feature information into the feature list. The data de-duplication method performed by the central processing unit  121  and the de-duplication circuit  124  may refer to the related description of  FIG. 2  or  FIG. 3 , which is not repeated hereinafter. 
     When the host  10  sends the read command, the central processing unit  121  can convert/decode the read command (containing the logical addresses) of the host  10  into a corresponding internal control command (containing the physical addresses of the non-volatile memory  110 ). According to the internal control signal, the memory control circuit  122  can address/control the non-volatile memory  110 , so as to read the codeword (the encoded data) from the non-volatile memory  110 . The ECC circuit  125  can execute the ECC algorithm to decode the codeword into the data and temporarily store the decoded data into the memory buffer  123 . Then, the central processing unit  121  can return the data temporarily stored in the memory buffer  123  to the host  10 . 
       FIG. 5  is a circuit block diagram illustrating the controller  120  depicted in  FIG. 1  according to another embodiment of the invention. In the embodiment shown by  FIG. 5 , the controller  120  includes a central processing unit  121 , a memory control circuit  122 , a memory buffer  123 , a de-duplication circuit  124  and an ECC circuit  125 . The central processing unit  121 , the memory control circuit  122 , the memory buffer  123 , the de-duplication circuit  124  and the ECC circuit  125  shown in  FIG. 5  may refer to the related description of  FIG. 4 , which is not repeated hereinafter. In the embodiment shown by  FIG. 5 , the de-duplication circuit  124  is coupled to the ECC circuit  125  for directly receiving the feature information generated by the ECC circuit  125 . 
     In summary, the non-volatile memory apparatus  100  and the data de-duplication method thereof described in the foregoing embodiments can generate the feature information corresponding to the raw data by reusing the existing ECC method. Upon comparing the feature information with feature list, the controller  120  can learn about whether the encoded data corresponding to the raw data has been written into the non-volatile memory  110 . As a result, the non-volatile memory apparatus  100  and the data de-duplication method thereof described in the foregoing embodiments are capable of reducing the number of times that the same encoded data is repeatedly written into the non-volatile memory  110 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.