Can anyone brief me the difference between Component object Model and Document Object Model and Elaborate what they are and how to use them
thanks a million
COM (Component Object Model) is a cross-language programming model for the Microsoft Windows platform based on interfaces inheriting from a common ancestor (IUnknown) providing a way to create, and then dynamically discover and use various software libraries (the components).
For example, the whole Windows Shell is a set of COM libraries, and the Windows Explorer makes uses of components to extend its default capabilities, for example to add new toolbars, or provide property sheets for various file types.
COM is a rather complicated technology to learn, full of pitfalls, and heavily based on the Windows registry and GUIDs (like... {21EC2020-3AEA-1069-A2DD-08002B30309D}).
It uses reference counting to handle the memory allocation and liberation of components.
COM provides several ways to instanciate those components, the various "threading models".
I invite you to read the wikipedia entry for COM, as there is much more to be said about it: http://en.wikipedia.org/wiki/Component_Object_Model
DOM is a completely unrelated technology.
Web pages in browsers are built upon SGML, and now XML based-languages, the HTML family.
These languages are hierarchical in the sense that they are comprised of container tags that in turn contain other tags.
<html>
<body>
<img src="t.jpg" />
</body>
</html>
The DOM (Document Object Model) is a standardized way of accessing this hierarchy via programming, either for reading, or for modification, usually by using languages like Javascript.
It also provides the various events that can be used to enhance web pages interactivity, like the "onclick", "onload" events...
The W3C has played a great role in standardizing this model, so that the various browsers can be (mostly) compatible and use the same javascript code to manipulate the DOM of pages.
COM is a form of IPC that runs on Microsoft Windows. DOM is a method for querying and manipulating HTML and XML documents.
Component Object Model is a Binary Interface standard for software introduced by Microsoft in 1993.
it is used to enable inter-process communication object creation in a large range of programming languages. Com is the basis of several other Microsoft technologies and frameworks, including OLE, OLE Automation, Browser Helper object, ActiveX the Windows shell, DirectX, UMDF, and Windows Runtime.
The essence of COM is a language-neutral way of implementing objects that can be used in environments different from the one in which they were created even across machine boundaries.
Related
We want to embed a 3D CAD viewer into our web-based collaboration platform. It would work similar to the one offered by Opencascade. You can see it here.
We do not charge for the use of our platform and we would prefer an open source option if it is available (Opencascade viewer is not open source).
Does Autodesk Forge have a similar offering?
Thanks!
CAD viewer solution for a WEB can be split into several pieces:
On-server converter of CAD model.
Conversion of CAD file into intermediate format. You might need a lot of Data Connectors in case if you need supporting wide range of CAD formats, or restrict functionality to import vendor-neutral formats like STEP.
Generation of Web-friendly triangulation-based 3D model. This step might include model simplification in case if you have to deal with large models.
Server backend implementing business logic and backend for 3D viewer. The complexity of 3D Viewer backend depends on functionality provided with it and ability of viewer to handle extra-large models. In simplest case, this might be just a file server providing 3D model in format like glTF.
Client part, e.g. HTML+JavaScript code for displaying 3D model using WebGL, as well as GUI and application-specific logic. The viewer might just display 3D model (in which case it is barely distinguishable from non-CAD viewers), or give many features like Shaded and Wireframe (not just mesh edges) modes, picking sub-parts, Clipping Boxes, clipping with capping, annotations, dimensions, explode view, HLR view, a bunch of them!
Although it is technically possible loading some small CAD models directly in the Browser, in general this task is expected to reside on server to improve user experience and give some protection to intellectual properties (of CAD models). The converter may be based on Open CASCADE Technology, which is an open source framework, in case if STEP/IGES input file formats are enough (output could be your custom file format or glTF 2.0, for instance). But in case of native CAD formats support (like CATIA and others) you will unlikely find any free open-source libraries.
The Web viewer itself relies on WebGL and normally can be based on any traditional JavaScript-based library like Three.js (or existing 3D Viewer on top), or may rely on C++-based engine (again, Open CASCADE Technology can be build as WebAssembly module). WebAssembly-based viewer may give some performance benefits and it is more friendly to C++ developers (but apparently - less friendly to JavaScript developers). There is a hidden issue, though, as many open-source C++ libraries commonly have LGPL license - pretty good for desktop, but might have legality issues in case of a Web application. In contrast, WEB-based libraries are normally more proprietary-friendly with permissible licenses ignoring open-source software ideas put into licenses like (L)GPL.
In general, 3D CAD Viewer definition is very wide, and requirements list in your question are very basic and unclear - just to embed 3D Viewer in your WEB application. You may write your own Web Viewer based on open source components, or consider commercial options already implementing features you are looking for, and aware of / providing some solutions for handling tricky problems.
Looks like Forge Viewer fits the bill perfectly and covers most of the features available with the demo ;)
You may experience/preview Viewer following this link using a model of your own here and follow here to build up a MVP here...
For the features that are not readily/built-in out of the box Viewer is highly extensible and offers API making it pretty straight forward to develop extensions following here and also the blogs/tutorials available here.
I have done a fair bit of Automation programming using Access to drive the operations of other Office programs. This has been straightforward because the references needed are specific Microsoft programs and I get help learning the type libraries from the Developer Reference Help pages and exploring the classes, methods, and properties in the object browser.
I've also used type libraries from Lotus Notes and Adobe Acrobat to integrate specific functions of those programs, but I needed to use SDKs to understand those objects and methods.
Now I'm looking to automate a web browser control in future projects. I can find specific code samples if I search very specific topics, like [vba] http post web form, but what I'm really looking for is a higher-level review of type libraries and active-X controls. I've found snippets of code using SHDocVw and MSHTML, but I am looking for some guidance on which type libraries to use in this area and how to explore other possibilities.
I have used the Web Browser control in Access 2010, which I believe uses the Microsoft Internet controls reference.
Please see the following screenshot for more information. Note the code changes the zoom of the Web Browser so that an image zooms to fit.
http://screencast.com/t/WsqWTlZRnh
The documentation I found referring to the object used is at the following location:
http://msdn.microsoft.com/en-us/library/aa752127(v=vs.85).aspx
Good look…
I want to develop a delphi application with an HTML/CSS graphical user interface, not necessarily running from within a web browser. I want to do this do create a richer graphical user interface with animations etc. and break away from normal VCL components / Windows look. Any suggestions?
HTML and CSS won't deliver animations or a Rich User Interface to your feet. Far from it in fact. Quite the opposite. You will need to invest in a toolkit to provide that sort of functionality and almost certainly involve JavaScript. And even if you don't want your eventual application hosted in a web browser, your application will itself have to host a web browser to render your HTML/CSS/JavaScript UI, and you will then have a much more difficult job of connecting your GUI to your application logic (unless you do actually embrace a web application architecture).
Delphi (or any Windows application development language for that matter) gets you much, much further down the road towards a more simply, effectively and quickly implemented Rich User Interface than HTML or CSS.
If you don't like the look and feel of the standard Delphi controls (which in essence is what you are saying) there are numerous alternative libraries available.
Also bear in mind however that when someone uses a Windows application they expect it to look and behave a certain way to a large extent. Using fancy, web based paradigm's in a desktop application simply for the sake of it is likely to confuse and frustrate users if taken too far.
I'm all for user interfaces breaking with convention where it leads to a more intuitive user interface, but simply being "prettier" does not necessarily lead in that direction and is just as misguided as dogmatically adhering to convention.
In one of my applications I have an an embedded browser and I have implemented the IDocHostUIHandler interface. This allows me to expose a COM object via the "GetExternal" method. I simply have a COM object that exposes methods and properties of my application which makes them available to the web pages hosted inside the embedded browser.
So the script in my web pages has lines like "external.DoSomething()" and "i=external.GetThisValue()". So, for example, behind button onclick events you can run a method of your application (implement in the main form, in the COM object itself, or whatever you like).
This site has lots of info on embedding a browser in your Delphi app:
http://www.delphidabbler.com/articles?article=22
It can certainly be cumbersome to implement a lot of this stuff and in many cases there are probably better options. But for my specific purpose I am able to offer a "home page" which can easily be modified to change its layout, look and even expose more (or less) functionality as required by myself or my users.
If you want a Delphi program with a better-looking interface, HTML is really not what you're looking for. What you really need are better-looking VCL controls.
Take a look at TMS Smooth Controls, for example. If you're on Delphi 2009 or 2010, you can get it as a free download here. That's one of many component libraries that can bring a slicker user interface to your program.
HTML / CSS offers some nice features which are (not yet?) available in Delphi and the VCL. They are also a good starting point for client/server programming, separating the user interface and the business logic is a key factor here.
One popular library for Delphi is the extpascal project:
ExtPascal is an Object Pascal (Delphi,
FreePascal/Lazarus) wrapper/binding
for Ext JS, a complete GUI Ajax
framework, made in JavaScript, for
Rich Internet Application (RIA)
development. ExtPascal lets you use
Ext JS from Object Pascal commands
issued by the server. It brings the
structure and strict syntax of the
Object Pascal for programming the web
browser. ExtPascal will wrap Draw2d
into future releases.
Some demos are online here and here.
p.s. and I really like the HTML / CSS support for element and font sizes in relative units (for exampe percent). Combined with browser zoom in / zoom out and WCAG, user interface ergonomy can not be much better.
HTML Option 1
If you relly want to use HTML+CSS(+JavaScript) to build a GUI, you can have a look at HTML Applications, a very fascinating concept from Microsoft. HTML Applications, .hta files, have been supported from Windows ME, if I remember correctly, and they are still supported on Windows 7.
You could create an HTML Application (i.e. an HTA file), and by so doing, creating a GUI using only HTML, CSS, and JavaScript. When the user double-clicks the HTA file, it will open like a program, but the GUI is entirely based on HTML; in fact, the entire Window is an Internet Explorer window in disguise.
And now comes the important part: you could create non-GUI Delphi applications (i.e., Delphi applications that are not console applications, but that have no forms either), and start them via hyperlinks (or JavaScript) from within your HTA GUI. (Well, it is probably better to create one such Delphi application, and use command-line arguments (ParamStrs) to communicate the desired action.)
Just an idea...
HTML Option 2
Alternatively, you could create a normal Delphi GUI application, but fill the entire main form with a TWebBrowser (a IE control), using Align := alClient. Then you could either load static HTML pages (stored in the Program Files folder or on the Internet), or you could use Delphi to dynamically create HTML pages to show. I think it is possible to intercept links from the control, so that you could respond to links using Delphi code.
What about OpenGL?
If you want to "break away" from the normal Windows look and feel, then I would recommend you to create your GUI using OpenGL. It is very easy to make a Delphi application with OpenGL (as long as you are familiar with OpenGL) - just add "OpenGL" to your uses list.
First this: I completely agree with Deltics' answer.
Having said that, if you master HTML and CSS (and JavaScript and AJAX etc etc) and you are looking for a way to use the power and speed of the Delphi compiler to run the dynamics of a website, this may be of interest.
I've created a project that uses the Delphi compiler to build a library that runs a website. The source-files combines HTML and Delphi, much like other web-scripting tools out there, but gets processed on a page-refresh, and compiled automatically. It uses a 'library handler' that plugs in the website library into pretty much anything you like: IIS, Apache, a stand-alone HTTP server (for hosting), or directly into InternetExplorer or FireFox (which is great for developing).
http://xxm.sourceforge.net/
New versions of Qt contain ability to use html/js for interfaces. I don't know if there is Qt library bindings for Delphi, but Qt is exactly what you want.
for Rich GUI and animation, have you looked at KSDev DXScen and VGScene ?
If you want to keep your delphi/Pascal Object 'background' and have a Web like RIA you also have a look to Morfik : link text
I am currently working on a design for a collection of subsystems, and I would like to be able to offer the API's exposed by a given subsystem for use by other subsystems.
In the past, I have used SWIG to expose C api's to a variety of other languages. This has worked well for me, but ultimately the API is defined in C. So basically one side of the API is language agnostic, and the other isn't.
What I would really like is to have something similar to SWIG that could generate the interface between 2 arbitrary languages based on some description of the API.
I don't want to use web services.
For example, I would like to call a 'function' from java, and implement the 'function' in Python. I'd like to be able to generate the language interop using a code generator.
Is there anything that exists which can do this today? At least for simple 'function' calls - ignoring the more complex cases like callbacks and situations where you need to maintain references outside of the 'function' call itself.
I found this after following gooli's link to Protocol Buffers .
This looks so compelling I'm going to propose it as an answer to my own question.
http://incubator.apache.org/thrift/
Thrift is a software framework for scalable cross-language services development. It combines a software stack with a code generation engine to build services that work efficiently and seamlessly between C++, Java, Python, PHP, Ruby, Erlang, Perl, Haskell, C#, Cocoa, Smalltalk, and OCaml.
From the whitepaper:
...we were presented with the challenge of building a transparent,
high-performance bridge across many
programming languages. We found that
most available solutions were either
too limited, did not offer sufficient
datatype freedom, or suffered from
subpar performance
Also from the whitepaper:
A. Similar Systems The following are software systems similar to Thrift.
Each is (very!) briefly described:
SOAP. XML-based. Designed for web services via HTTP, excessive XML
parsing overhead.
CORBA. Relatively comprehensive, debatably overdesigned and
heavyweight. Comparably cumbersome
software installation.
COM. Embraced mainly in Windows client softare. Not an entirely open
solution.
Pillar. Lightweight and high-performance, but missing
versioning and abstraction.
Protocol Buffers. Closed-source, owned by Google. Described in Sawzall
paper.
The last part about Protocol Buffer's is out-of-date - its been open sourced
COM (and to a lesser extent Firefox's XPCOM) might be what you are looking for. In COM, you define the API using a language called IDL which can then be compiled into different languages. When using the same language the calls usually degenerate into efficient function calls.
However, COM is a very complex and dying piece of technology that I would never use for a new project.
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I need some resources that talk about how to design your software to be extensible, i.e. so that other people can write add-ons/plug-ins that adds functionality to it.
What do you recommend? Any books out there that discuss the subject?
I would prefer something that's short and to the point; a bit of theory and a bunch of concrete examples.
I'm not targeting a specific language, I want to be able to understand the core idea so that I can implement it in any language.
And for the same reason, I prefer not to do it using a framework that someone else built (unless the framework is not very high-level, i.e. doesn't hide too much), at the moment I only want to educate myself on the subject and experiment with various ways to implement it. Plus, a framework usually assumes user's knowledge about the subject.
UPDATE
I'm not asking about OOP or allowing my classes to be inherited. I'm talking about designing an application that will be deployed on a system, such that it can be extended by third-party add-ons AFTER its been deployed.
For example, Notepad++ has a plug-in architecture where you can place a .dll file in the plugins folder, and it adds functionality to the application that wasn't there, such as color-picking, or snippet insertion, or many other things (a wide range of functionality).
IF we're talking .NET, try Scripting .NET applications with VBScript over on CodeProject. Lots of concrete examples there.
Below are sites implementing various application extension techniques
ClearScript - Makes V8, VBScript and JScript available to .NET apps
CS-Script - The C# Script Engine
Plugin Architecture using C#
Opinio plugin architecture
Notes on the Eclipse Plug-in Architecture
Plug-in Architecture Framework for Beginners
Gecko plugin architecture
Fungimol plugin architecture
OSGI is a good practical example of a technical framework allowing to do what you are after.
The theory is here.
The (free!) book is there.
Extensibility and the ability to write plugin must deal with service lifecycle
adding / removing service/plugin on the spot
managing dependencies between services
managing states of services (declared, installed, started, stopped,...)
What is OSGI for ?
One of the main functions of a module is as a unit of deployment… something that we can either build or download and install to extend the functionality of our application.
You will find a good introduction here, on the central notion of service (which is related to your question, and which explain some problems around services, key component for extensibility).
Extract:
Why are services then so important if so many applications can be built without them? Well, services are the best known way to decouple software components from each other.
One of the most important aspects of services is that they significantly minimize class loading problems because they work with instances of objects, not with class names. Instances that are created by the provider, not the consumer. The reduction of the complexity is quite surprising
Not only do services minimize configuration, they also significantly reduce the number of shared packages.
Implement SOLID principles in your application.
1. Single responsibility principle: A class should have only a single responsibility (i.e. only one potential change in the software's specification should be able to affect the specification of the class
2.Open/closed principle: Software entities … should be open for extension, but closed for modification
3. Liskov substitution principle: Objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program
4. Interface segregation principle: Many client-specific interfaces are better than one general-purpose interface
5. Dependency inversion principle: One should Depend upon Abstractions. Do not depend upon concretions
Stackoverflow questions:
Example of Single Responsibility Principle
Is the Open/Closed Principle a good idea?
What is the Liskov Substitution Principle?
Interface Segregation Principle- Program to an interface
What is the Dependency Inversion Principle and why is it important?
You try to reach two competing goals:
The components of your software must expose a lot of themselves, so they can be reused
The components of your software must expose very little of themselves, so they can be reused
Explanation: To encourage code reuse, you should be able to extend existing classes and call their methods. This isn't possible when the methods are declared "private" and the classes are "final" (and can't be extended). So to meet this goal, everything should be public and accessible. No private data or methods.
When you release the second version of your software, you will find that many of the ideas of version 1 were plain wrong. You need to change many interfaces or your code, method names, delete methods, break the API. If you do this, many people will turn away. So in order to be able to evolve your software, the components must not expose anything that is not absolutely necessary - at the cost of code reuse.
Example: I wanted to observe the position of the cursor (caret) in an SWT StyledText. The caret is not meant to be extended. If you do it, you'll find that the code contains checks like "is this class in the package org.eclipse.swt" and a lot of methods are private and final and whatnot. I had to copy about 28 classes out of SWT into my project just to implement this feature because everything is locked down.
SWT is a nice framework to use and hell to extend.
Of course there is the famous Open Closed Principle - http://en.wikipedia.org/wiki/Open/closed_principle
Well it depends on the language.
In C/C++ I'm pretty sure there is a loadlibrary function that allows you to open a library at runtime and invoke it's exported functions. This is typically how it's done in C/C++.
In .NET, there is Reflection, which is offers similar (but more broad) to loadlibrary. There is also entire libraries built on Reflection like Managed Extension Framework, or Mono.Addins that does most of the heavy lifting for you already.
In Java, there is also Reflection. And there is the JPF (Java Plugin Framework) which is used in stuff like Eclipse IIRC.
Depending on what language you use I could recommend some tutorial/books. I hope this was helpful.
Plugin architecture is becoming very popular for its extensibility and thus flexibility.
For c++, Apache httpd server is actually plugin based, but a concept of module is used instead. Most of apache features are implemented as modules, like cache, rewrite, load balancing, and even threading model. It is a very modular software I ever saw.
And for java, Eclipse is definitely plugin based. The core of Eclipse is an OSGI module system which manage bundles, another concept for plugin. Bundle can provide extension points on which we can build modules with less efforts. The most intricate thing in OSGI is its dynamic characteristic, which means bundles can be installed or uninstalled at runtime. No stop-the-world syndrome any more!
Since I dont have enough rep points to leave a comment, I am posting this as an answer. SharpDevelop is an IDE for developing applications in C#/VB.NET/Boo. It has a pretty impressive architecture that allows itself to be extended in a number of ways - right from new menu items to development support for whole new languages.
It uses a bit of XML configuration to act as a glue layer between a core of the IDE and the plugin implementation. It handles locating, loading and versioning of plugins out of the box. Deploying new plugins is matter of simply copying in the new xml configuration file and the required assemblies (DLLs) and restarting the application. You can read more on this in the book "Dissecting a csharp application" by the original author(s) - Christian Holm, Mike Krüger, Bernhard Spuida of the application from here. The book doesnt seem to be available on that site, but i found a copy that might still be around here
Also found a related question here
Checkout "CAB" - Microsoft's Composition Application Building blocks Framework. I think they've got a "web version" of that too...
I have just started to develop a smart client application. These are two options I am considering.
Using Microsoft's System.AddIn namespace. Looks very promising, however it may be a little complex for our end solution.
Or the Smart Client - Composite UI Application Block from Microsoft
Recently, i have looked at taking components both the Composite UI Application Block and the System.AddIn namespace to build my own. Since source code is available for the CAB it is easy to extend. I think our end solution will be a light weight version of the CAB, definatly using the Unity Application Block
If you work with .Net, our research yielded two approaches: scripting and composition.
Scripting
You extend the functionality of what your classes can do by orchestrating them using scripts. That means exposing what is compiled in your favorite .Net language in a dynamic language.
Some options we found worth exploring:
IronPython
IronRuby
JavaScript: Jint, Jurassic and JavaScript .Net are good starting points.
Script.Net -> this one was the first one to call our attention.
Composition
If you start a project with .Net 4 or above, you must take a good look at the Managed Extensibility Framework (MEF). It allows you to extend the functionality of your apps in a plugin way.
The Managed Extensibility Framework (MEF) is a composition layer for
.NET that improves the flexibility, maintainability and testability of
large applications. MEF can be used for third-party plugin
extensibility, or it can bring the benefits of a loosely-coupled
plugin-like architecture to regular applications.
Managed Add-in Framework is also a good read.
MSDN: http://msdn.microsoft.com/en-us/library/dd460648.aspx
Codeplex: http://mef.codeplex.com/
Rather than re-inventing the wheel, use the frameworks in hand. Eclipse and Netbeans both support plugin based extensions. You have to work in Java though.