c# barcode generator open source TREE-STRUCTURED DATA in Font

Creator QR Code 2d barcode in Font TREE-STRUCTURED DATA

CHAPTER 14 TREE-STRUCTURED DATA
Denso QR Bar Code Printer In None
Using Barcode generator for Font Control to generate, create QR Code 2d barcode image in Font applications.
www.OnBarcode.com
Code 128 Code Set C Creator In None
Using Barcode maker for Font Control to generate, create Code 128C image in Font applications.
www.OnBarcode.com
record type might not be a parent as I defined that term near the beginning of this chapter, because it might not actually have any children. For example, a given offering might have no students enrolled in it at this time. Just as a given node in the type tree corresponds to many nodes in each of many occurrence trees (in general), so a given edge in the type tree corresponds to many edges in each of many occurrence trees (again in general). In fact, an edge in the type tree can be thought of as representing a one-to-many relationship (where many includes the zero case). Another difference between these IMS-style heterogeneous trees and the homogeneous trees discussed in earlier sections is that those homogeneous trees were of potentially unlimited depth. For example, a given part might explode to any number of levels. By contrast, the depth of an IMS-style type tree is fixed (it s three in the education example), and the depth of any corresponding occurrence tree is equal to or less than that of the type tree. Although IMS-style trees can still be regarded as having an element of recursion in their make-up, that fact is much less important than it was for homogeneous trees, precisely because (a) different nodes are of different types, and (b) there s a limit on the depth, in the case of heterogeneous trees. As an aside, it s ironic to note, given the state of affairs just explained, that IMS or what subsequently became IMS, at any rate was originally intended precisely to address the bill-ofmaterials problem! Only later was it extended to become the general-purpose system that it was marketed as by IBM. As should be clear from the discussions in this chapter, IMS-style trees are not well suited to bill-of-materials not least because, in general, part-structure trees aren t true trees anyway and the machinations one has to go through in order to use IMS-style trees for the purpose are, to my mind, baroque in the extreme. See the paper A Hierarchic System: IMS in my book Relational Database Writings 1991 1994 (Addison-Wesley, 1995), for further discussion of this topic. One final remark: I haven t bothered to show the internal structure of the various record types and occurrences in Figures 14-11 and 14-12. For the sake of subsequent discussion, however, I ll assume that: Courses have a course number and title. Offerings have an offering number, a date, and a location. Teachers have just an employee number. Students have an employee number and a grade.
Paint UPC A In None
Using Barcode generation for Font Control to generate, create UPC-A Supplement 2 image in Font applications.
www.OnBarcode.com
Create Barcode In None
Using Barcode creator for Font Control to generate, create Barcode image in Font applications.
www.OnBarcode.com
I ve concentrated on IMS in this section so far for definiteness. For the record, however, let me now observe that (a) containment hierarchies as found in the world of object orientation and (b) XML documents (in which there is so much current interest) are both essentially occurrence trees in the sense discussed above. It follows that:
Make Code 39 Extended In None
Using Barcode maker for Font Control to generate, create Code 3 of 9 image in Font applications.
www.OnBarcode.com
QR Code Creator In None
Using Barcode generator for Font Control to generate, create Quick Response Code image in Font applications.
www.OnBarcode.com
CHAPTER 14 TREE-STRUCTURED DATA
Making Barcode In None
Using Barcode drawer for Font Control to generate, create Barcode image in Font applications.
www.OnBarcode.com
USD-4 Printer In None
Using Barcode drawer for Font Control to generate, create Ames code image in Font applications.
www.OnBarcode.com
Everything I ve said or will say in this chapter regarding IMS-style trees applies equally well, mutatis mutandis, to containment hierarchies and XML documents as well. Relational systems can provide XML-like functionality if desired (because they can certainly provide IMS-like functionality, as I ll show in a moment). With respect to both object and XML databases, we re sad to say revisiting a lot of ancient territory (though I have to say too that most of the current literature doesn t seem to recognize this fact). The semistructured data model, on which XML is supposed to be based, is essentially just the old IMS data model in a different guise. But now I m beginning to stray from the principal topic of the present chapter; let me leave these issues for some future publication (which I do plan to produce as soon as I can).
Draw Quick Response Code In None
Using Barcode generation for Office Word Control to generate, create QR image in Microsoft Word applications.
www.OnBarcode.com
QR Code JIS X 0510 Encoder In C#
Using Barcode creation for .NET Control to generate, create QR Code ISO/IEC18004 image in VS .NET applications.
www.OnBarcode.com
The usual technique for representing IMS-style trees relationally is well known, of course; indeed, it was discussed by Codd himself in his famous 1970 paper A Relational Model of Data for Large Shared Data Banks (CACM 13, No. 6, June 1970). The technique isn t worth discussing in detail here; in essence, all it involves is simply (a) extending each record type (i.e., each node) in the type tree with the key of its parent, if any, and then (b) mapping each resulting record type to a separate relvar. In the case of the type tree of Figure 14-12, this process yields the following relvars (in outline): COURSE { COURSE#, TITLE } KEY { COURSE# } OFFERING { COURSE#, OFF#, DATE, LOCATION } KEY { COURSE#, OFF# } FOREIGN KEY { COURSE# } REFERENCES COURSE TEACHER { COURSE#, OFF#, EMP# } KEY { COURSE#, OFF#, EMP# } FOREIGN KEY { COURSE#, OFF# } REFERENCES OFFERING STUDENT { COURSE#, OFF#, EMP#, GRADE } KEY { COURSE#, OFF#, EMP# } FOREIGN KEY { COURSE#, OFF# } REFERENCES OFFERING PREREQ { MAJOR_COURSE#, MINOR_COURSE# } KEY { MAJOR_COURSE#, MINOR_COURSE# } The usual techniques for mapping IMS-style operations on IMS-style trees into relational analogs are equally straightforward, and I omit further discussion here.
Data Matrix ECC200 Generator In None
Using Barcode printer for Online Control to generate, create DataMatrix image in Online applications.
www.OnBarcode.com
Generating EAN13 In Visual Studio .NET
Using Barcode drawer for .NET Control to generate, create EAN 13 image in Visual Studio .NET applications.
www.OnBarcode.com
UPC A Recognizer In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Barcode Generation In Objective-C
Using Barcode generation for iPhone Control to generate, create Barcode image in iPhone applications.
www.OnBarcode.com
Quick Response Code Creation In Objective-C
Using Barcode creation for iPhone Control to generate, create QR Code ISO/IEC18004 image in iPhone applications.
www.OnBarcode.com
Data Matrix Recognizer In Visual Basic .NET
Using Barcode reader for .NET framework Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
Barcode Drawer In Java
Using Barcode printer for Java Control to generate, create Barcode image in Java applications.
www.OnBarcode.com
Paint GTIN - 128 In None
Using Barcode drawer for Office Word Control to generate, create GTIN - 128 image in Office Word applications.
www.OnBarcode.com
Scan EAN13 In Visual Studio .NET
Using Barcode decoder for VS .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
ANSI/AIM Code 128 Creator In Java
Using Barcode drawer for Java Control to generate, create Code 128 Code Set B image in Java applications.
www.OnBarcode.com
Copyright © OnBarcode.com . All rights reserved.