NetBeans Architecture Answers for org.netbeans.modules.xml.xdm module

General Information

Question (arch-what): What is this project good for?
Answer: The XDM module provides a basis for tool ready XML language models that require full document fidelity, undo/redo, and the ability to sync with the underlying source.

List of the main features:

• Support for full document fidelity. The users text including spacing and comments are preserved.
• Undo / Redo is supported using the concept of an immutable tree. XDM nodes do not have parent pointers (only a pointer to the model). Thus a node can be in multiple trees, where each tree is a version. When a mutation to the tree occurs a clone is made of each node in the parent path from the root to the mutated node. All unchanged nodes are simply referenced and thus will live in multiple trees. Thus an undo / redo is simply a reference change. The cost of storing multiple tree is minimized as only the diffs are stored in each version of the tree.
• The visitor pattern is used in addition to the DOM interfaces which allows easier tree walking
• An XML diff visitor supports XML difference. Element identity can be supplied by the client.
Question (arch-overall): Describe the overall architecture.
Answer:

XDM (XML Document Model) provides a XAM based full fidelity XML model which implements the org.w3c.dom interfaces. The intention is not to provide an an alternate implementation of the dom interfaces but only to reuse part of the api where it makes sense and more importantly provide a foundation on which to provide a model basis for graphical multi way editors.

This module was developed to support the following requirements:
• Full document fidelity. This allows the original document to be preserved and only changes the actual sections of the document which were mutated (i.e. the transformation is lossless).
• Support for undo/redo in a memory efficient way
• Support for diff to allow changes to be detected in the underlying source
• Visitor support
org.netbeans.modules.xml.xdm - This package provides API's for obtaining an XDM document and mutating the XDM tree. org.netbeans.modules.xml.xdm.diff - XML diff capabilities are exposed through this package. org.netbeans.modules.xml.xdm.nodes - XDM based implementation of DOM interfaces. org.netbeans.modules.xml.xdm.xam - XAM model and component abstractions based on XDM tree. This is the basis for XML language models (like WSDL, Schema, and BPEL). org.netbeans.modules.xml.xdm.visitor - Visitors for operations over the XDM such as generating XPath expressions, calculatin document position and finding elements by position.
Question (arch-usecases): Describe the main use cases of the new API. Who will use it under what circumstances? What kind of code would typically need to be written to use the module?
Answer:

The typical client of XDM would be a tool author supporting an XML language who wants to provide a custom client API. A concrete example of this is the XML Schema model. The XML Schema model starts by subclassing AbstractXDMModel and providing the component updater, which is called in conjunction with sync to mutate the model according to changes in the underlying source.

WSDL model

The WSDL model is based on the XDM model and relies on the XDM capabilities to provide the infrastructure necessary for providing a XAM based model.

Schema model

The Schema model is based on the XDM model and relies on the XDM capabilities to provide the infrastructure necessary for providing a XAM based model.

BPEL model

The BPEL model is based on the XDM model and relies on the XDM capabilities to provide the infrastructure necessary for providing a XAM based model. The XDM model can be used in standalone mode. BaseDocument sd = ...; Lookup lookup = Lookups.singleton(sd); // create an editable ModelSource with base document // in the lookup (this is required) ModelSource ms = new ModelSource(lookup, true); // create an XDMModel XDMModel model = new XDMModel(ms); // sync the XDM model with the underlying source model.sync(); // create customer element, same as dom Element customer = model.getDocument().createElement("customer"); // add to the model as 0th child of employee element, not shown model.add(employee,customer,0);
Question (arch-time): What are the time estimates of the work?
Answer:

This module is implementation complete, but will require additional effort for ongoing maintenence in conjunction with the other modules.

Question (arch-quality): How will the quality of your code be tested and how are future regressions going to be prevented?
Answer:

This module is covered by JUnit tests and findBugs has been incorporated into the development process. This module is the core of most of the domain models and is extensively covered.

Question (arch-where): Where one can find sources for your module?
Answer:

The sources for the module are in NetBeans CVS in xml/xdm directory.

Project and platform dependencies

Question (dep-nb): What other NetBeans projects and modules does this one depend on?
Answer:

These modules are required in project.xml file:

• org.netbeans.modules.editor.lib - The module is needed for compilation. The module is used during runtime. Specification version 1.7.1.1 is required.
• org.netbeans.modules.xml.core - The module is needed for compilation. The module is used during runtime. Specification version 1.9.1.4 is required.
• org.netbeans.modules.xml.text - The module is needed for compilation. The module is used during runtime.
• org.netbeans.modules.xml.xam - The module is needed for compilation. The module is used during runtime. Specification version 1.1 is required.
• org.openide.util - The module is needed for compilation. The module is used during runtime. Specification version 6.8.1 is required.
Question (dep-non-nb): What other projects outside NetBeans does this one depend on?
Answer:

none

Question (dep-platform): On which platforms does your module run? Does it run in the same way on each?
Answer:

100% java, no platform requirement.

Question (dep-jre): Which version of JRE do you need (1.2, 1.3, 1.4, etc.)?
Answer:

1.5

Question (dep-jrejdk): Do you require the JDK or is the JRE enough?
Answer:

jre is sufficient

Deployment

Question (deploy-jar): Do you deploy just module JAR file(s) or other files as well?
Answer:

only module jar file

Question (deploy-nbm): Can you deploy an NBM via the Update Center?
Answer:

yes

Question (deploy-shared): Do you need to be installed in the shared location only, or in the user directory only, or can your module be installed anywhere?
Answer:

installed anywhere

Question (deploy-packages): Are packages of your module made inaccessible by not declaring them public?
Answer:

currently friends support is being used, thus all clients are known.

Question (deploy-dependencies): What do other modules need to do to declare a dependency on this one?
Answer:

This module is only exposing friend api's, thus a friend entry must be added to this module before use.

Compatibility with environment

Question (compat-i18n): Is your module correctly internationalized?
Answer:

yes

Question (compat-standards): Does the module implement or define any standards? Is the implementation exact or does it deviate somehow?
Answer:

This module implements the DOM interfaces but is not intended to be a replacement for DOM. This module has special semantics surrounding mutation and thus the full DOM interfaces are not supported.

Question (compat-version): Can your module coexist with earlier and future versions of itself? Can you correctly read all old settings? Will future versions be able to read your current settings? Can you read or politely ignore settings stored by a future version?
Answer:

no settings or user visible features.

Access to resources

Question (resources-file): Does your module use java.io.File directly?
Answer:

no

Question (resources-layer): Does your module provide own layer? Does it create any files or folders in it? What it is trying to communicate by that and with which components?
Answer:

there is an empty layer.

Question (resources-read): Does your module read any resources from layers? For what purpose?
Answer:

no

Question (resources-mask): Does your module mask/hide/override any resources provided by other modules in their layers?
Answer:

no

Lookup of components

Question (lookup-lookup): Does your module use org.openide.util.Lookup or any similar technology to find any components to communicate with? Which ones?
Answer:

no

Question (lookup-register): Do you register anything into lookup for other code to find?
Answer:

no

Question (lookup-remove): Do you remove entries of other modules from lookup?
Answer:

no

Execution Environment

Question (exec-property): Is execution of your code influenced by any environment or Java system (System.getProperty) property?
Answer:

no

Question (exec-component): Is execution of your code influenced by any (string) property of any of your components?
Answer:

no

Question (exec-ant-tasks): Do you define or register any ant tasks that other can use?
Answer:

no

Question (exec-classloader): Does your code create its own class loader(s)?
Answer:

no

Question (exec-reflection): Does your code use Java Reflection to execute other code?
Answer:

no

Question (exec-privateaccess): Are you aware of any other parts of the system calling some of your methods by reflection?
Answer:

no

Question (exec-process): Do you execute an external process from your module? How do you ensure that the result is the same on different platforms? Do you parse output? Do you depend on result code?
Answer:

no

Question (exec-introspection): Does your module use any kind of runtime type information (instanceof, work with java.lang.Class, etc.)?
Answer:

The casting is documented. This needs to be reviewed and cleaned up. We need to look at each instanceof, AssignableFrom, and cast to see if we can eliminate this using a) visitor b) JDK 1.5 return value override

Question (exec-threading): What threading models, if any, does your module adhere to?
Answer:

This model has been synchronized for thread safety. Thread safety is supported by allowing only a single model mutation (using java synchronized keyword). The immutable nature of the model only requires synchronization when updating the tree thus synchronization of nodes which are not yet in the tree is not thread safe.

Question (security-policy): Does your functionality require modifications to the standard policy file?
Answer:

no

Question (security-grant): Does your code grant additional rights to some other code?
Answer:

no

Format of files and protocols

Question (format-types): Which protocols and file formats (if any) does your module read or write on disk, or transmit or receive over the network? Do you generate an ant build script? Can it be edited and modified?
Answer:

This module is designed to read and write XML files through a swing document.

Question (format-dnd): Which protocols (if any) does your code understand during Drag & Drop?
Answer:

none

Question (format-clipboard): Which data flavors (if any) does your code read from or insert to the clipboard (by access to clipboard on means calling methods on java.awt.datatransfer.Transferable?
Answer:

none

Performance and Scalability

Question (perf-startup): Does your module run any code on startup?
Answer:

no

Question (perf-exit): Does your module run any code on exit?
Answer:

no

Question (perf-scale): Which external criteria influence the performance of your program (size of file in editor, number of files in menu, in source directory, etc.) and how well your code scales?
Answer:

The size of the XML file both in terms of the number of bytes as well as the number of elements and attributes.

Question (perf-limit): Are there any hard-coded or practical limits in the number or size of elements your code can handle?
Answer:

no. This module is able to parse large schemas > 1MB.

Question (perf-mem): How much memory does your component consume? Estimate with a relation to the number of windows, etc.
Answer:

A basic populated model is about 8000 bytes, this depends on how many components and the size of the file.

Question (perf-wakeup): Does any piece of your code wake up periodically and do something even when the system is otherwise idle (no user interaction)?
Answer:

no

Question (perf-progress): Does your module execute any long-running tasks?
Answer:

This module is used by clients and thus does not react directly to user events.

Question (perf-huge_dialogs): Does your module contain any dialogs or wizards with a large number of GUI controls such as combo boxes, lists, trees, or text areas?
Answer:

no

Question (perf-menus): Does your module use dynamically updated context menus, or context-sensitive actions with complicated and slow enablement logic?
Answer:

no

Question (perf-spi): How the performance of the plugged in code will be enforced?
Answer:

Client code providing element identity may impact the performance of sync. However, invoking sync is done by the client as thus the impact will be reflected in the client module. There is no direct user interaction in this module.