Canonical Design Blog: Design museum exhibition London
Something exciting Next year
Bruno Maag from Dalton Maag has been asked by the Design Museum London to put on an exhibition of his work. This is a collaboration between ourselves and DM,
the exhibition will be in two parts a substantial part of which will be featuring the Ubuntu font.
Does anyone have any favorite mobile tech sites they want me to look at while I'm considering the next phase of mobile redesign?
My idea is to build a new mobile design without using any forum framework (do not use vBulletin, XenForo, etc.) and do not use any big SPA Javascript frameworks (do... (2 Replies)
Hi all,
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I need to create a script to automate creating a deployment for me by taking into consideration two input files.
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I've notepad in which logs are present. I need to design a web page by which if some one paste their ticket number and click on "search" the logs for that ticket number should be displayed at the bottom.
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Hi,
I am working on a project to develop an embedded device that can transfer files between two usb devices ( pen drives). We are using an NUC950A ARM9 microcontroller and we've put the Linux 2.1 kernel on the development board and it works. Can i use nano -x to design my own GUI so that i can run... (3 Replies)
i want to design the shell for some basic commands such as cp mkdir rm mv etc... so please let me know how to start and wich all books to refer and if any body is having the model just mail me at, devskamat018@gmail.com:) i will be waiting please reply soon (1 Reply)
i want to make a shell program.
This program i give a current day and the result is to appear
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Can anybody tell me what is the best website or books to read for getting good knowledge in doing C++ class design. Please leave cplusplus.com or bjorne stroustrup. Other than these is there any website or book. Please do tell me (0 Replies)
Alzabo::Design(3pm) User Contributed Perl Documentation Alzabo::Design(3pm)NAME
Alzabo::Design - Documentation on Alzabo's design
DESCRIPTION
This document describes some of the Alzabo's design.
ARCHITECTURE
There are objects representing the schema, which contains table objects. Table objects contain column, foreign key, and index objects.
Column objects contain column definition objects. A single column definition may be shared by multiple columns, but has only one owner.
This is a diagram of these inheritance relationships:
Alzabo::* (::Schema, ::Table, ::Column, ::ColumnDefinition, ::ForeignKey, ::Index)
/
is parent to
/
Alzabo::Create::* Alzabo::Runtime::*
This a diagram of how objects contain other objects:
Schema - makes--Alzabo::SQLMaker subclass object (many)
/
contains contains--Alzabo::Driver subclass object(1)
|
Table (0 or more) Alzabo::RDBMSRules subclass object(1)
/ (* Alzabo::Create::Schema only)
/
contains--------------------
/
/
ForeignKey Column (0 or more) Index (0 or more)
(0 or more) |
contains
|
ColumnDefinition(1)
Note that more than one column may share a single definition object (this is explained in the "Alzabo::Create::ColumnDefinition" documenta-
tion). This is only relevant if you are writing a schema creation interface.
Other classes
* "Alzabo::Driver"
These objects handle all the actual communication with the database, using a thin wrapper over DBI. The subclasses are used to imple-
ment functionality that must be handled uniquely for a given RDBMS, such as creating new values for sequenced columns.
* "Alzabo::SQLMaker"
These objects handle the generation of all SQL for runtime operations. The subclasses are used to implement functionality that varies
between RDBMS's, such as outer joins.
* "Alzabo::RDBMSRules"
These objects perform several funtions. First, they validate things such as schema or table names, column type and length, etc.
Second they are used to generate SQL for creating and updating the database and its tables.
And finally, they also handle the reverse engineering of an existing database.
* "Alzabo::Runtime::Row" and "Alzabo::Runtime::RowState::*"
The "Alzabo::Runtime::Row" class represents a single row. These objects are created by "Alzabo::Runtime::Table", "Alzabo::Run-
time::RowCursor", and "Alzabo::Runtime::JoinCursor" objects. It is the sole interface by which actual data is retrieved, updated, or
deleted in a table.
The various "RowState" classes are used in order to change a row's behavior depending on whether it is live, live and cached, poten-
tial, or deleted.
* "Alzabo::Runtime::JoinCursor" and "Alzabo::Runtime::RowCursor"
These objects are cursor that returns row objects. Using a cursor saves a lot of memory for big selects.
* "Alzabo::Runtime::UniqueRowCache"
Loading this class turns on Alzabo's simple row caching mechanism.
* "Alzabo::Config"
This class is generated by Makefile.PL during installation and contains information such as what directory contains saved schemas and
other configuration information.
* "Alzabo::ChangeTracker"
This object provides a method for an object to register a series to backout from multiple changes. This is done by providing the
ChangeTracker object with a callback after a change is succesfully made to an object or objects. If a future change in a set of opera-
tions fail, the tracker can be told to back the changes out. This is used primarily in "Alzabo::Create::Schema".
* "Alzabo::MethodMaker"
This module can auto-generate useful methods for you schema, table, and row objects based on the structure of your schema.
* "Alzabo::Exceptions"
This object creates the exception subclasses used by Alzabo.
WHY THE SUBDIVISION BETWEEN Alzabo::*, Alzabo::Create::*, and Alzabo::Runtime::*?
There are several reasons for doing this:
o In some environments (mod_perl) we would like to optimize for memory. For an application that uses an existing schema, all we need is
to be able read object information, rather than needing to change the schema's definition. This means there is no reason to have the
overhead of compiling all the methods used when creating and modifying objects.
o In other environments (for example, when running as a separately spawned CGI process) compile time is important.
o Many people using Alzabo will use the schema creation GUI and then write an application using that schema. At the simplest level, they
would only need to learn how to instantiate "Alzabo::Runtime::Row" objects and how that class's methods work. For more sophisticated
users, they can still avoid having to ever look at documentation on methods that alter the schema and its contained objects.
RATIONALE FOR CURSORS
Using cursors is definitely more complicated. However, there are two excellent reasons for using them: speed and memory savings. As an
example, I did a test with the old code (which returned all its objects at once) against a table with about 8,000 rows using the "Alz-
abo::Runtime::Table->all_rows" method. Under the old implementation, it took significantly longer to return the first row. Even more
importantly than that, the old implementation used up about 10MB of memory versus about 4MB! Now imagine that with a 1,000,000 row table.
Thus Alzabo uses cursors so it can scale better. This is a particularly big win in the case where you are working through a long list of
rows and may stop before the end is reached. With cursors, Alzabo creates only as many rows as you need. Plus the start up time on your
loop is much, much quicker. In the end, your program is quicker and less of a memory hog. This is good.
AUTHOR
Dave Rolsky, <autarch@urth.org>
perl v5.8.8 2007-12-23 Alzabo::Design(3pm)