barcode add-in for excel Byte-string representation of variable-length records in Software

Creating Code 128 Code Set C in Software Byte-string representation of variable-length records

Byte-string representation of variable-length records
Generating Code 128 Code Set C In None
Using Barcode maker for Software Control to generate, create ANSI/AIM Code 128 image in Software applications.
Recognizing Code 128 In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition
Make Code 128 In Visual C#.NET
Using Barcode creator for .NET Control to generate, create Code 128 Code Set A image in .NET framework applications.
Generate Code 128 Code Set B In .NET
Using Barcode maker for ASP.NET Control to generate, create Code 128 image in ASP.NET applications.
IV Data Storage and Querying
Making Code-128 In Visual Studio .NET
Using Barcode encoder for VS .NET Control to generate, create Code 128 Code Set A image in .NET framework applications.
Draw Code-128 In Visual Basic .NET
Using Barcode maker for .NET framework Control to generate, create Code 128 Code Set B image in .NET applications.
11 Storage and File Structure
Bar Code Printer In None
Using Barcode creator for Software Control to generate, create barcode image in Software applications.
Generating USS-128 In None
Using Barcode generator for Software Control to generate, create GTIN - 128 image in Software applications.
The McGraw Hill Companies, 2001
UPCA Generator In None
Using Barcode maker for Software Control to generate, create UPC Code image in Software applications.
Making ECC200 In None
Using Barcode printer for Software Control to generate, create DataMatrix image in Software applications.
11
Code128 Creator In None
Using Barcode maker for Software Control to generate, create Code128 image in Software applications.
Draw GS1 - 13 In None
Using Barcode creation for Software Control to generate, create GS1 - 13 image in Software applications.
Storage and File Structure
Encoding Code 9/3 In None
Using Barcode maker for Software Control to generate, create Code 93 Full ASCII image in Software applications.
Generating Code 3 Of 9 In Objective-C
Using Barcode maker for iPhone Control to generate, create Code 39 Extended image in iPhone applications.
Block Header Size # Entries Location Free Space
UCC - 12 Encoder In VS .NET
Using Barcode generator for Visual Studio .NET Control to generate, create USS-128 image in .NET framework applications.
Create ECC200 In Java
Using Barcode creator for Java Control to generate, create ECC200 image in Java applications.
Records
Code 39 Extended Drawer In Java
Using Barcode generator for Java Control to generate, create Code-39 image in Java applications.
GS1 - 12 Generator In Java
Using Barcode maker for Java Control to generate, create UPC-A Supplement 2 image in Java applications.
End of Free Space
Data Matrix 2d Barcode Recognizer In .NET
Using Barcode scanner for .NET Control to read, scan read, scan image in .NET framework applications.
Making Code 128C In None
Using Barcode generation for Font Control to generate, create Code 128 Code Set A image in Font applications.
Figure 1111 Slotted-page structure
sentation, called the slotted-page structure, is commonly used for organizing records within a single block The slotted-page structure appears in Figure 1111 There is a header at the beginning of each block, containing the following information: 1 The number of record entries in the header 2 The end of free space in the block 3 An array whose entries contain the location and size of each record The actual records are allocated contiguously in the block, starting from the end of the block The free space in the block is contiguous, between the nal entry in the header array, and the rst record If a record is inserted, space is allocated for it at the end of free space, and an entry containing its size and location is added to the header If a record is deleted, the space that it occupies is freed, and its entry is set to deleted (its size is set to 1, for example) Further, the records in the block before the deleted record are moved, so that the free space created by the deletion gets occupied, and all free space is again between the nal entry in the header array and the rst record The end-of-free-space pointer in the header is appropriately updated as well Records can be grown or shrunk by similar techniques, as long as there is space in the block The cost of moving the records is not too high, since the size of a block is limited: A typical value is 4 kilobytes The slotted-page structure requires that there be no pointers that point directly to records Instead, pointers must point to the entry in the header that contains the actual location of the record This level of indirection allows records to be moved to prevent fragmentation of space inside a block, while supporting indirect pointers to the record
11622 Fixed-Length Representation
Another way to implement variable-length records ef ciently in a le system is to use one or more xed-length records to represent one variable-length record There are two ways of doing this: 1 Reserved space If there is a maximum record length that is never exceeded, we can use xed-length records of that length Unused space (for records
Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition
IV Data Storage and Querying
11 Storage and File Structure
The McGraw Hill Companies, 2001
File Organization
0 1 2 3 4 5
Perryridge Round Hill Mianus Downtown Redwood Brighton
A-102 A-305 A-215 A-101 A-222 A-217
400 350 700 500 700 750
A-201
A-218
A-110
File of Figure 1110, using the reserved-space method
shorter than the maximum space) is lled with a special null, or end-of-record, symbol 2 List representation We can represent variable-length records by lists of xedlength records, chained together by pointers If we choose to apply the reserved-space method to our account example, we need to select a maximum record length Figure 1112 shows how the le of Figure 1110 would be represented if we allowed a maximum of three accounts per branch A record in this le is of the account-list type, but with the array containing exactly three elements Those branches with fewer than three accounts (for example, Round Hill) have records with null elds We use the symbol to represent this situation in Figure 1112 In practice, a particular value that can never represent real data is used (for example, an account number that is blank, or a name beginning with * ) The reserved-space method is useful when most records have a length close to the maximum Otherwise, a signi cant amount of space may be wasted In our bank example, some branches may have many more accounts than others This situation leads us to consider the linked list method To represent the le by the linked list method, we add a pointer eld as we did in Figure 119 The resulting structure appears in Figure 1113
0 1 2 3 4 5 6 7 8
Copyright © OnBarcode.com . All rights reserved.