Patent Publication Number: US-9836284-B2

Title: HTML5 graph layout for application topology

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is related to U.S. patent application Ser. No. 14/307,997, entitled “HTML5 Graph Overlays for Application Topology,”, and to U.S. patent application Ser. No. 14/307,981, entitled “Connection Paths for Application Topology”, all of which are assigned to the assignee of this application, have been filed on the same day of this application, and the entire contents of which are incorporated by reference herein. 
     BACKGROUND 
     HyperText Markup Language 5 (HTML5) is an increasingly popular markup language used for structuring and presenting content for the World Wide Web. One component of HTML5 is Scalable Vector Graphics (SVG), which is an XML-based vector image format for describing two-dimensional graphics applications and images, and a set of related graphics script interfaces. While SVG is a powerful graphic specification, SVG lacks native support for a layout mechanism. As a result, a developer must specify absolute positions and sizes for all SVG elements, including text, images, backgrounds, and shapes, within the elements&#39; containers. Manually specifying these absolute positions and sizes greatly reduces developer productivity and raises the cost of application maintenance. As such, there are challenges for developers seeking to create a web-based graphical user interface that renders complex graphical topologies and figures. 
     SUMMARY 
     Accordingly, one or more embodiments provide a Scalable Vector Graphics (SVG) layout engine that parses declarative layout configurations and translates the declarative layout into SVG elements to render complex graphical topologies. In one example use case, the SVG layout engine may generate a graphical user interface (GUI) for creating application blueprints that specify an application&#39;s architecture, including virtual machines (VM) nodes, software services and application components within the VM nodes. The application blueprints define the structure of the application, enable the use of standardized application infrastructure components, and specify installation dependencies and default configurations. The application blueprints define the topology for deployment in an infrastructure-agnostic manner to be portable across different cloud computing environments. The SVG layout engine dynamically calculates absolute positions and sizes of child elements based on the declarative layout to visually represent the application blueprint. 
     Embodiments of the present disclosure provide a method of generating a user interface. The method includes retrieving structural information comprising a topology of virtual computing resources and application components executing thereon. The structural information specifies a plurality of nodes corresponding to the virtual computing resources and a plurality of child elements of the plurality of nodes. The method further includes generating a declarative layout associated with the plurality of child elements of the plurality of nodes according to the structural information, and generating a plurality of scalar vector graphics (SVG) elements that renders the plurality of child elements based on the declarative layout. The method includes rendering, on a display device, a graphical user interface comprising the plurality of SVG elements, wherein the graphical user interface visually represents the topology. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited aspects are attained and can be understood in detail, a more particular description of embodiments of the invention, briefly summarized above, may be had by reference to the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  depicts a system for generating a blueprint of an application to be deployed in a cloud computing environment, according to one embodiment of the present disclosure. 
         FIG. 2  illustrates an example graphical user interface for specifying an application blueprint for an application to be deployed. 
         FIG. 3  is a flow diagram of a method for generating a graphical user interface of an application for specifying a logical topology, according to one embodiment of the present disclosure. 
         FIG. 4  is a block diagram depicting a layout model for child elements within a node specified by one or more item declarations, according to one embodiment of the present disclosure. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
       FIG. 1  depicts a system  100  for generating a blueprint of an application to be deployed in a cloud computing environment, according to one embodiment of the present disclosure. Via user input selections, a client application  102  interacts with an application director  108  to generate a blueprint  126  that specifies a logical topology of an application  136  to be deployed. Client application  102  and application director  108  may be software applications running in different hosts and/or virtual machines (not shown) in a client-server relationship, or on a same host or virtual machine (VM). In one embodiment, application director  108  may be a web-based application that may be accessed via client application  102 , e.g., a web browser, although other implementations may be used. Client application  102  may be configured to render a graphical user interface (GUI)  140  on a display device (not shown) communicatively connected to the host and/or virtual machine on which client application  102  executes. 
     In one embodiment, client application  102  includes a graph layout manager  104  and a Scalable Vector Graphics (SVG) layout engine  106  configured to render a blueprint  126  for creation of a new blueprint or modification of an existing blueprint in a GUI  140  of client application  102 . In one embodiment, graph layout manager  104  may be responsible for the position and sizing of overall blueprint layouts, line connections, cross-node dependencies. SVG layout engine  106  may be responsible for relative position of text and decoration within each node. In one embodiment, graph layout manager  104  and SVG layout engine  106  may be client-side libraries of scripting code provided by application director  108  and executable by client application  102  to programmatically render graphical elements of GUI  140  on a display device. In some implementations, e.g., where application director  108  is a web-based application, graph layout manager  104  and SVG layout engine  106  are JavaScript libraries downloaded from application director  108  to render a GUI  140  comprised of web documents, e.g., HTML, SVG, Cascading Style Sheets (CSS). For example, when a user directs client application  102  to access a Uniform Resource Locator (URL) pre-assigned to application director  108 , application director  108  may return in response web documents (e.g., HTML, CSS, SVG), client-side code (e.g., JavaScript, in-line or linked files) which may include graph layout manager  104  and SVG layout engine  106 , and multimedia files (e.g., GIFs, Flash, MPEGs) that client application  102  uses to render GUI  140 . While the present disclosure describes functions performed by each of client application  102  and application director  108 , it should be recognized that other embodiments may differently distribute functions between client application  102  and application director  108 , i.e., shift functionality to server-side or client-side. 
     In operation, a user (e.g., software developer) may access application director  108  via client application  102  to design a topology for and orchestrate deployment of a multi-tier application  136  onto one of deployment environments  112  provided by a cloud computing platform provider  110 . In one implementation, the user may utilize a graphical user interface provided by application director  108  to assemble and arrange items from a catalog into an application blueprint  126 , for an application to be deployed, that includes a logical topology of virtual computing resources and application components for supporting application  136 . Cloud computing platform provider  110  (sometimes referred to simply as “cloud provider”) may provide multiple deployment environments  112 , for example, for development, testing, staging, and production of the application. Services may be accessed from cloud computing platform provider  110 , for example, via REST (Representational State Transfer) APIs (Application Programming Interface) or any other client-server communication protocol. One particular implementation of a REST API for cloud computing services is vCloud Director API available from VMware, Inc. Cloud computing platform provider  110  provisions virtual computing resources (e.g., virtual machines, or “VMs,”  114 ) to provide a deployment environment  112  in which the user can deploy its multi-tier application. One particular example of a deployment environment is one implemented using cloud computing services from a vCloud DataCenter available from VMware, Inc. 
     In one embodiment, application director  108  includes the following software modules: a topology generator  120 , a deployment plan generator  122 , and a deployment director  124 . Topology generator  120  generates a blueprint  126  that specifies a logical topology of the application  136  to be deployed. As mentioned earlier, blueprint  126  generally captures the structure of an application  136  as a collection of application components executing on virtual computing resources. 
     Blueprint  126  provides a visual representation of an applications&#39; architecture, including, in one embodiment, one or more virtual machines (VMs) nodes, software services within the VM nodes, executable components within the VM nodes or software services. Blueprint  126  further provides a visual representation of component dependency connections. The dependency connections represent the architectural relationship between blueprint components and affect various lifecycles of the application. For instance, if a service A depends on service B, during deployment, the installation and configuration of service A will be waiting for the completion of service B. In some embodiments, blueprint  126  may visually represent one or more logical networks, for example, via visual aids to conventionally distinguish and manage logical networks between VM nodes. 
     For example, blueprint  126  generated by application director  108  for an online store application may specify a web application (e.g., in the form of a Java web application archive or “WAR” file comprising dynamic web pages, static web pages, Java servlets, Java classes, and other property, configuration and resources files that make up a Java web application) executing on an application server (e.g., Apache Tomcat application server) and that uses as a database (e.g., MongoDB) as a data store. It is recognized that the term “application” is used herein to generally refer to a logical deployment unit, comprised of application packages and their dependent middleware and operating systems. As such, in the example described above, the term “application” may refer to the entire online store application, including application server and database components, rather than just the application logic of the web application itself. 
     Blueprint  126  may be assembled out of items from a catalog  130 , which is a listing of available virtual computing resources (e.g., VMs, networking, storage) that may be provisioned from cloud computing platform provider  110  and available application components (e.g., software services, scripts, code components, application-specific packages) that may be installed on the provisioned virtual computing resources. Catalog  130  may be pre-populated and customized by an administrator (e.g., IT or system administrator) that enters in specifications, configurations, properties, and other details about each item in catalog  130 . Blueprint  126  may define one or more dependencies between application components to indicate an installation order of the application components during deployment. For example, since a load balancer usually cannot be configured until a web application is up and running, the user may specify a dependency from an Apache service to an application code package. 
     Deployment plan generator  122  of application director  108  generates a deployment plan  128  based on blueprint  126  that includes deployment settings for blueprint  126  (e.g., virtual computing resources&#39; cluster size, CPU, memory, networks) and an execution plan of tasks having a specified order in which virtual computing resources are provisioned and application components are installed, configured, and started. Deployment plan  128  provides an IT administrator with a process-oriented view of blueprint  126  that indicates discrete steps to be performed to deploy application  136 . Different deployment plans  128  may be generated from a single blueprint  126  to test prototypes (e.g., new application versions), to scale-up and scale down deployments, or deploy application  136  to different deployment environments  112  (e.g., testing, staging, production). 
     Deployment director  124  of application director  108  executes deployment plan  128  by communicating with cloud computing platform provider  110  via a cloud interface  132  to provision and configure VMs  114  in a deployment environment  112 , as specified by deployment plan  128 . Cloud interface  132  provides a communication abstraction layer by which application director  108  may communicate with a heterogeneous mixture of cloud provider  110  and deployment environments  112 . Deployment director  124  provides each VM  114  with a series of tasks specific to the receiving VM  114  (herein referred to as a “local deployment plan”). The tasks may be scripts that are executed by VMs  114  to install, configure, and/or start one or more application components. For example, a task may be a script that, when executed by a VM  114 , causes VM  114  to retrieve and install particular software packages from a central package repository  134 . Deployment director  124  coordinates with VMs  114  to execute the tasks in an order that observes installation dependencies between VMs  114  according to deployment plan  128 . After application  136  has been deployed, application director  108  may be utilized to monitor and modify (e.g., scale) the deployment. 
       FIG. 2  illustrates an example graphical user interface  140  for specifying a blueprint  126  for an application to be deployed. GUI  140  includes a canvas  202  that provides a graphical view of a blueprint  126  as a schematic diagram of application  136 . GUI  140  may include one or more “palettes” that display items from catalog  130  that are available for use in creating a blueprint. Canvas  202  is configured to provide drag-and-drop functionality that enables the user to select and drag an item from the palettes and drop the selected item within the boundaries of canvas  202  to insert the selected item into blueprint  126 , as illustrated by arrow  210 . 
     In one embodiment, graph layout manager  104  is configured to generate one or more “nodes”  212 , which visually represent virtual computing resources (e.g., a virtual machine, or a cluster of virtual machines) configured according to a user&#39;s selection. Graph layout manager  104  may be configured to initially generate nodes for GUI  140  upon first loading of GUI  140 , and may be configured to modify GUI  140  to add, remove, or modify the nodes responsive to user input (e.g., user drags in a new VM). SVG layout engine  106  is configured to generate graphical elements that render contents of node  212  in GUI  140  according to techniques described herein. 
     In the embodiment shown in  FIG. 2 , GUI  140  includes a first palette  204  that lists logical templates defined in and available from catalog  130 , a second palette  206  that lists software services defined in and available from catalog  130 , and a third palette  208  that lists types of code components that may be inserted into a blueprint. A blueprint may include any resource, and a resource can be any of virtual machines, guest operating systems, application services, any network/storage resources (e.g., load balancers, storage arrays), or other software resources like Active Directory entries. 
     A blueprint may include one or more instances of logical templates, which specify virtual computing resources for a virtual machine, such as CPU, memory, networking, storage, guest operating system, pre-installed installed runtime environments (e.g., Java Runtime Environment), and application services and commands (e.g., ssh, wget). For example, one logical template may specify a virtual machine having a 2 GB of RAM, a dual-core CPU, and pre-installed guest operating system CentOS version 5.6 supporting 32-bit architecture, while another logical template may specify a virtual machine having Red Hat Enterprise Linux 6.1 supporting 64-bit architecture. Logical templates enable application director  108  to define an application topology in a cloud-agnostic manner. In some embodiments, the logical templates may be mapped to virtual machine templates made available by cloud provider  110  (referred to herein as “cloud templates”.) 
     In one example, to create a blueprint that models a three-tiered application, a user may select three items from palette  204  of logical templates, drag the items onto canvas  202 , and create three nodes representing each tier of the application. In the example shown in  FIG. 2 , a three-tiered application with a database backend, an application server, and a load balancer is visually represented by three nodes  212  (labeled as “load_balancer,” “app_server,” and “database”). Each node  212  has been created from a logical template (identified as “CentOS32 5.6”) having CentOS 5.6 32-bit operating system installed. 
     A blueprint  126  may further include one or more application components, such as software services and code components, to be installed on a virtual machine for supporting execution of an application. Code components refer to application-specific binaries, scripts, or processes, for example, written by a developer and packaged into one or more files, to provide logic for the application. In catalog  130 , code components are represented as types or formats of scripting and application code. Examples of types of code components include Java Archive (JAR) files, Java Enterprise Archive (EAR) files, Java web application archive (WAR) files, Ruby Gems packages, SQL scripts, and other suitable modules of scripting logic. Services are scripted software that provide a software infrastructure for an application, and are generally reused in multiple applications. Examples of services include application servers (e.g., Rails, Apache Tomcat, JBoss), database servers (e.g., GemFire, MySQL, SQLFire, MongoDB, Postgres), monitoring services (e.g., Hyperic, SpringInsight), web servers (e.g., Apache, VMware vFabric Enterprise Ready Server), messaging services (e.g., RabbitMQ), and other middleware services. 
     In one embodiment, application components may be added to a node  212  within canvas  202  to specify which application components are to execute on the node. For example, the user may select an application component (e.g., code component, software service) from palettes  206 ,  208  and drag the item into a node  212  within canvas  202  to specify the node should have the selected item executing therein. In the example three-tiered application in  FIG. 2 , a user has added a MySQL database item, a JBoss application server, and an Apache web server from palette  206  of services to nodes  212 . Each node may host multiple application components. Some application components, such as services, may host, execute, and/or deploy certain application components themselves, such as code components. In the three-tiered application example above, the user specifies an application component packaged as an EAR file (identified as “bank_app”) as being deployed in the JBoss application server. In another example, the user may specify an SQL script (identified as “init_db_script”) that is executed by the MySQL database to initialize the database. 
     In one embodiment, graph layout manager  104  may be configured to render deployment-related dependencies  216 ,  218  between application components and/or nodes within canvas  202 . The user may select two application components within canvas  202  using a pointer cursor in GUI  140 , and create a dependency between the application components via a link button  220 . It is appreciated that the user may later use a pointer cursor to select an existing dependency and delete and/or modify the selected dependency, for example, by pressing a delete button  222 . In the three-tiered application example shown in  FIG. 2 , a dependency from the Apache load balancer to code component (e.g., “bank_app”) is depicted by dashed arrow  216  and represents that the Apache load balancer should be deployed after the installation of the code component (e.g., “bank_app”) is completed. Similarly, a second dependency (depicted by dashed arrows  218 ) from the code component (e.g., “bank_app”) to the database initialization script (e.g., “init_db_script”) is created to represent that the code component (e.g., “bank_app”) should wait until the database node, the database service, and the SQL script initializing the database have all been run before continuing. 
     In one embodiment, blueprint  126  is rendered using Scalable Vector Graphics (SVG), which is an XML-based vector image format supported by web browsers and other applications (e.g., client application  102 ). While SVG is a powerful graphics specification, SVG lacks the native support of a sophisticated layout mechanism. All SVG elements are absolutely positioned and sized within their SVG containers. For a complex blueprint, manually specifying the positions and sizes of each child element (e.g., text, images, backgrounds) may greatly increase software development costs of applications having topology generators (e.g., an application director  108 ) and make code of such applications difficult to maintain. It is recognized that, while embodiments herein are described in detail using SVG, the disclosed techniques for generating a graphical user interface may be applied using other image formats including other vector-based formats and raster-based formats. 
     Accordingly, in one or more embodiments, SVG layout engine  106  is configured to parse a declarative layout configuration and translate the declarations into actual SVG elements that render content within a node  212 . SVG layout engine  106  is configured to determine positional informational for child elements within a node  212 , and generate SVG elements including text, images, and graphic shapes that visually represent the child elements within each node  212 , using the determined positional information. 
       FIG. 3  is a flow diagram of a method  300  for generating a graphical user interface of an application (e.g., application director  108 ) for specifying a logical topology, according to one embodiment of the present disclosure. Method  300  for generating a GUI may be performed in response to user input requesting to create a new blueprint  126  or modify an existing blueprint  126 . While method  300  is described in conjunction with the system shown in  FIG. 1 , it is recognized that other systems may be utilized to perform the method described herein. 
     At step  302 , graph layout manager  104  retrieves from application director  108  structural information associated with a blueprint. The structural information specifies a logical topology comprised of nodes, application components within the nodes, and deployment dependencies between the application components and/or the nodes. In one implementation, graph layout manager  104  may retrieve structural information formatted in a JavaScript Object Notation (JSON) format via a REST API provided by application director  108 , although other data formats and other techniques for transmitting data may be utilized. 
     In one example, the structural information associated with the example blueprint shown in  FIG. 2  may be a data structure containing a first entry corresponding to a first node (“load_balancer”), a second entry corresponding to a second node (“app_server”), and a third entry corresponding to a third node (“database”). Each entry may specify the content within the corresponding node. For example, the first entry may specify a label associated with the first node (“load 13  balancer”), the logical template associated with the first node (“CentOS32 5.6”), and any application components contained within the first node, such as the software service Apache Load Balancer. Content within a node may be specified in a nested manner, i.e., as child elements of the node parent element. For example, the second entry corresponding to the second node may include a child element corresponding to the application component JBoss Application Server, which itself includes a child element corresponding to a code component (“bank_app”). 
     At step  304 , graph layout manager  104  of client application  102  determines positional information of nodes in blueprint  126  based on the structural information. In one embodiment, where the structural information is contained an array-like data structure, graph layout manager  104  steps through each entry in the structural information and assigns a logical position to each node within canvas  202 . A logical position as used herein refers to abstract positional information distinguished from pixel-based coordinate values. For example, graph layout manager  104  may process the structural information and assign a first logical position at (0,0) to the first node, a second logical position at (0,1) to the second node, and a third logical position at (0,2) to the third node. Graph layout manager  104  may further iterate through each level in the structural information and specify logical positions for content within each node. For example, the Apache load balancer component within the first node may be assigned a first logical position (0,0) relative to the first node. 
     At step  306 , graph layout manager  104  generates one or more SVG container elements for the nodes based on the determined positional information. Each SVG container element may correspond to a node. In one implementation, graph layout manager  104  generates an &lt;svg&gt; element that creates an SVG document fragment which may exist inside another document, such as an HTML document, or canvas  202 , and which has its own viewport and coordinate system. In other implementations, other SVG container or structural elements, such as the &lt;g&gt; element used to group together elements, may be used. In one embodiment, graph layout manager  104  determines and sets absolute positions of the SVG containers within canvas  202 . 
     As used herein, generating an SVG element (e.g., container elements, shapes, graphics elements, text content elements) may refer to using client-side scripting code to programmatically generate and/or modify an object inserted into a Document Object Model (DOM) of GUI  140 . For example, a method call such as createElement(namespace, “svg”) may be used to instantiate an SVG element of a specified tag (e.g., “svg”). A method call such as setAttribute(“x”, value) may be used to specify or dynamically modify one or more attributes of an SVG element. A method call such as appendChild( ) may be used to dynamically insert the SVG element into the DOM for rendering. It is recognized that client application  102  may be configured to automatically re-render GUI  140  or portion of GUI  140  on the display device in response to changes (e.g., insertions) to the DOM. While the described techniques may be implemented using programmatic manipulation of SVG elements, it is understood that, in some embodiments, generating an SVG element may include generation of markup text including one or more tags (e.g., &lt;svg&gt;, &lt;/svg&gt;, &lt;polygon&gt;, etc.) and the one or more attributes that define the SVG element. 
     At step  308 , graph layout manager  104  generates a declarative layout for child elements of the nodes based on structural information  116 . The child elements in a node and the layout of those child elements may be specified in a list of item declarations. In one embodiment, the item declarations associated with the child elements in the nodes may be generated by graph layout manager  104  while processing the structural information (i.e., in step  304 ). For example, in one implementation, graph layout manager  104  may traverse structural information  116 , and responsive to encountering a particular type of topology component (e.g., node, software service, code component, etc.), generate and insert a corresponding item declaration for that type of topology component into a growing data structure to build a declarative layout. In other embodiments, the item declarations associated with the child elements in the nodes may be contained in the structural information as retrieved from application director  108 . An example declarative layout for content in the nodes is shown in Table 1 below. While Table 1 depicts one particular syntax for item declarations formatted as a JSON data structure, it is understood that other syntaxes and data structure formats may be used. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Sample item declarations 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 01 
                 [ { 
               
            
           
           
               
               
               
            
               
                   
                 02 
                 gtype: ‘rect’, 
               
               
                   
                 03 
                 width: ‘100%’, 
               
               
                   
                 04 
                 height: ‘100%’, 
               
               
                   
                 05 
                 attrs: { 
               
            
           
           
               
               
               
            
               
                   
                 06 
                 stroke: ‘black’ 
               
            
           
           
               
               
               
            
               
                   
                 07 
                 } 
               
            
           
           
               
               
               
            
               
                   
                 08 
                 }, { 
               
            
           
           
               
               
               
            
               
                   
                 09 
                 layout: { 
               
            
           
           
               
               
               
            
               
                   
                 10 
                 type: ‘vbox’, 
               
               
                   
                 11 
                 margin: 5 
               
            
           
           
               
               
               
            
               
                   
                 12 
                 }, 
               
               
                   
                 13 
                 items: [ { 
               
            
           
           
               
               
               
            
               
                   
                 14 
                 gtype: ‘text’, 
               
               
                   
                 15 
                 attrs: { 
               
               
                   
                 16 
                  text: ‘Line 1’ 
               
               
                   
                 17 
                 } 
               
            
           
           
               
               
               
            
               
                   
                 18 
                 }, { 
               
            
           
           
               
               
               
            
               
                   
                 19 
                 gtype: ‘text’, 
               
               
                   
                 20 
                 attrs: { 
               
               
                   
                 21 
                  text: ‘Line 2’ 
               
               
                   
                 22 
                 } 
               
            
           
           
               
               
               
            
               
                   
                 23 
                 } ] 
               
            
           
           
               
               
               
            
               
                   
                 24 
                 } ] 
               
               
                   
                   
               
            
           
         
       
     
     The example shown in Table 1 includes a first item declaration (i.e., lines  02 - 07 ) specifying a box, and a second item declaration specifying two lines of text within the box (i.e., lines  09 - 23 ). Item declarations may be defined in a hierarchical manner, such that one item declaration can contain “child” item declarations. For example, the second item declaration contains two sub-items corresponding to a first line of text (i.e., lines  13 - 18 ) and a second line of text (i.e., lines  18 - 23 ). 
     At step  310 , SVG layout engine  106  parses the declarative layout and determines positional and sizing information for the child elements based on the declarative layout. SVG layout engine  106  may determine absolute positions, heights, and widths for each child element in a node based on the declarative layout. In one implementation, SVG layout engine  106  performs multiple passes on the declarative layout, for example, by first calculating heights and widths of elements, then calculating absolute positions of those elements as offset by the heights and widths of neighboring elements. The absolute positions of an SVG element may be specified as X-axis and Y-axis coordinate values relative to an ancestor SVG container element corresponding to a node, or in some embodiments, relative to canvas  202 . For example, the absolute positions of an SVG element within a node may be specified relative to a coordinate system having an (0,0) location at the upper left corner of a node, such that X-axis coordinates increase rightward and Y-axis coordinates increase downward, although other coordinate systems may be used. It is understood that while the present disclosure may express positional information and sizing information in terms of pixel values, other units of measurement may be used, such as centimeters, millimeters, inches, picas, points, units relative to the default font size (i.e., em), units relative to the height of a particular font character (i.e., ex). 
     &lt;rect width=“100” height=“100” stroke=“black” fill=“none”&gt;&lt;/rect&gt; 
     &lt;text x=“5” y=“16” width=“90”&gt;Line 1&lt;/text&gt; 
     &lt;text x=“5” y=“36” width=“90”&gt;Line 2&lt;/text&gt; 
     Table 2: Sample SVG Document Based on Item Declarations 
     Assuming an SVG container component size is 100 ×100, SVG layout engine  106  may translate the example item declarations of Table 1 into the SVG document shown above in Table 2 . To create the resultant SVG document, SVG layout engine  106  calculates the absolute positions and sizes of child elements based on properties specified by the item declarations, e.g., width, height, and margin properties. SVG layout engine  106  determines a 100-pixel width and height for the &lt;rect&gt; element based on the “width:100%” and “height:100%” specified in the item declaration. SVG layout engine  106  further determines the absolute position of “x=5” for the text elements based on the “margin: 5 ” specified in the item declaration. SVG layout engine  106  further determines the absolute position of “y=16” for the first text element, and determines the absolute position of “y=36” for the second text element, which accounts for the margin (i.e.,  5 ) and the height of the first text element (i.e., 20) preceding the second text element. It is recognized that the text elements have a Y-coordinate of “16” and “36” instead of “5” and “25” because SVG text element&#39;s Y-coordinate starts with their baseline instead of their top by default, and SVG layout engine  106  automatically offsets the text based on the text element&#39;s height. The SVG elements shown in Table 2 are rendered to display two lines of text within a box  402 , as depicted in  FIG. 4 . 
     Each item declaration may specify a plurality of properties for the associated child element, which are used in translating the declaration into actual SVG elements. A graphics type property (e.g., “gtype”) specifies a type of graphical element the item declaration is associated with. In some embodiments, the graphics type property corresponds to a specific SVG element, e.g., a “rect” graphics type declares the item as an SVG rectangular shape element (&lt;rect&gt;); a “text” graphics type declares the item as an SVG text content element (&lt;text&gt;) element. It is recognized that the graphics type property does not necessarily have a strict one-to-one mapping with particular SVG elements, and does not necessarily assign a property value that is the same as the SVG tag, and that the graphics types may define a logical type that ultimately maps to any, including multiple, SVG element(s). 
     In one embodiment, an item declaration may include one or more attribute properties (e.g., “attrs”) specifying attribute values for SVG elements. SVG layout engine  106  parses the attribute properties and may include the attribute values directly into the SVG element. Some attribute values may be “passed” through directly to the resultant SVG element, such as the “stroke:‘black’” attribute (i.e., line  06  of Table 1) of the &lt;rect&gt; element. In another example, SVG layout engine  106  parses a text attribute property specifying the textual data of the respective text element (i.e., lines  16  and  21  of Table 1), and inserts the textual data as the SVG text element&#39;s content. 
     In one embodiment, an item declaration may specify a layout property indicating a type of layout for determining positional information of one or more associated child elements in sequence. The layout property may specify a directional layout (e.g., horizontal, vertical) where child elements within that layout are positioned one after another in sequence in a particular direction, for example, in a top-to-bottom direction for a vertical layout, and in a left-to-right direction for a horizontal layout. SVG layout engine  106  calculates the absolute position of each child element as the position of a previous child element offset by at least the dimensions of the previous child element. 
     For example, SVG layout engine  106  parses the second item declaration in Table 1 specifying a vertical layout (i.e., “type: ‘vbox’”) and calculates the position of the second line of text to be the position of the first line of text offset vertically by at least the height of the first line of text. In another example, SVG layout engine  106  may parse an item declaration specifying a horizontal layout (e.g., “type: ‘hbox’”) and calculates the position of a child element to be the position of the previous child element offset horizontally by at least the width of the previous child element. It is understood that other types of layouts may be utilized. In some embodiments, if no layout is explicitly specified, a pre-determined default layout may be applied. For example, a default layout (i.e., “type: ‘auto’”) places the child element using absolute positions within the current container. Even with absolute positioning, the child element may take advantage of dynamic layout calculation to support width and height in percentage of parent dimensions and margins. 
     In some embodiments, the layout property may specify one or more sub-properties that are applied to the positioning of all child elements associated with the layout property. The layout property may include a margin property that applies a margin around all child elements associated with the layout property. For example, in response to parsing the second item declaration in Table 1 specifying a margin property of 5 pixels (i.e., line  11 : “margin:  5 ”), SVG layout engine  106  calculates the position of a child element to be the position of the previous child element offset vertically by a 5 pixel margin in addition to the height of the previous child element. In some embodiments, the layout property may specify an alignment value (e.g., “align: center”) which enables one or more child elements to be horizontally or vertically and/or left- , center- , or right-aligned within its respective container. In response to parsing an item declaration containing an alignment property, SVG layout engine  106  may calculate a position of a child element based on the position and size of the child element&#39;s parent element and further based on the calculated size of the child element itself For example, for a horizontally-centered child element, SVG layout engine  106  may calculate the position of the child element based on 50% of the width of the parent element offset by 50% of the width of the child element itself. 
     In one embodiment, as item declarations may be nested within other item declarations, it is recognized that layouts may be nested within other layouts.  FIG. 4  is a block diagram depicting a layout model for child elements within a node specified by one or more item declarations. A node  404  rendered within canvas  202  includes a polygon shape  420 , and a header portion  406 , a main portion  408 , a footer portion  410  and line shapes  424  arranged in a vertical layout. Child elements of header portion  406  having a horizontal layout (depicted as a box  412 ) is nested within an overall vertical layout (depicted as a box  414 ) for portions  406 ,  408 ,  410 . For example, header portion  406  includes title text  416  (“AppServer”) positioned according to a horizontal layout. Child elements within main portion  408  may also have its own layout (depicted as box  422 ) for positioning application components, depicted as a combination of rectangular elements and text elements “ISS_with.NET”, “.NET_4.0”, and “SQL_Server”. In the example shown, the item declaration for child elements within main portion  408  specify a horizontally centered layout for the application components. Child elements within footer portion  410  includes template text (“WIN64 V6.1.7601”) indicating the logical template associated with the node positioned according to another horizontal layout. 
     In one embodiment, SVG layout engine  106  may be configured to support layout flex, where remaining space in a node is dynamically allocated to child elements based on their respective flex value. An item declaration may specify a flex value that indicates a weighted value relative to other flex values according to which sizing information for an element is changed (i.e., “flexed”) based on any remaining space. SVG layout engine  106  may increase (or even decrease) the size of a child element by a proportion of remaining space based on the child element&#39;s flex value relative to the total flex value of all child elements. For example, a first child element with a flex value of “2” among two other child elements having a flex value of “1” would have its width increased by an amount of 50% of the remaining space. Flex values may include both horizontal and vertical flex values for allocating remaining space to widths and heights of child elements, respectively. 
     In one embodiment, SVG layout engine  106  may be configured to support automatic text truncation based on the text size and dimensions of the text&#39;s parent elements. SVG layout engine  106  may determine that an item declaration associated with a text element specifies a text truncation property (e.g., “text-trunc: ellipsis”). SVG layout engine  106  then determines whether the full text within the text element as rendered according to a given text size would exceed the boundaries of the text element&#39;s parent element(s). If so, SVG layout engine  106  truncates a portion of the full text such that that text element does not exceeds the boundaries, taking into account margins and other layout requirements. SVG layout engine  106  generates an SVG text element having the truncated text, and optionally includes an ellipsis character or other indication that the text has been truncated. 
     Referring back to  FIG. 3 , at step  312 , SVG layout engine  106  generates a plurality of SVG elements having absolute positions and sizes based on the determined positional information. SVG layout engine  106  generates one or more SVG elements having attributes specified according to the determined positional and sizing information. In one embodiment, for each item declaration, SVG layout engine  106  may call a method such as createElement(&lt;tagname&gt;) to instantiate a SVG element of a specified tag (e.g., “text”, “rect”) based on the graphics type property specified by the item declaration. SVG layout engine  106  may call a method, e.g., setAttribute(&lt;name&gt;, &lt;value&gt;), that sets position attributes (e.g., “x”, “y”) and size attributes (e.g., “height”, “width”) of the generated SVG element according to the determined positional and sizing information. SVG layout engine  106  may call a method call, e.g., appendChild(child) that inserts the generated SVG element into the node for rendering. 
     At step  314 , graph layout manager  104  determines positional information of dependencies between application components within the blueprint, if any. In response to SVG layout engine  106  calculating positional and sizing information for child elements within the nodes, graph layout manager  104  may proceed to determine positional information for drawing shapes (e.g., lines, arrows) connecting child elements within a node and child elements between nodes. In other words, after SVG layout engine  106  has finished calculating the absolute positions of a first application component and a second application component, graph layout manager  104  may determine where to draw a line connecting the application components that visually represents a dependency between the application components, such as dependency  218  shown in  FIG. 2 . 
     At step  316 , graph layout manager  104  generates one or more SVG element(s) indicating the dependencies between application components and/or nodes of the blueprint. The generated SVG elements that visually represent the dependencies may include the determined positional information. For example, graph layout manager  104  may generate an SVG line element having “x 1” and “y1” attributes associated with a starting position of the dependency and “x2” and “y2” attributes associated with an ending position of the dependency. 
     At step  318 , client application  102  renders, on a display device, a GUI  140  including the plurality of generated SVG elements representing an application blueprint, which includes SVG containers, SVG elements corresponding to child elements of the nodes, and SVG elements indicating deployment dependencies. It is recognized that, rather than generate the GUI entirely at once, client application  102  may render portions of GUI  140  comprising subsets of the generated SVG elements in an iterative manner and/or in an intermittent manner as SVG elements are generated according to method  300  (e.g., after steps  306 ,  312 ,  316 , etc.) 
     While embodiments disclosed herein are discussed with regards to generating an initial GUI for a blueprint, operations for modifying an existing GUI based on changes to the blueprint may be performed utilizing techniques described herein. In one embodiment, graph layout manager  104  may detect a change to application blueprint  126  in response to user input. For example, a user may insert a new node into canvas  202 , remove an existing node from canvas  202 , insert a new application component within a node, move an application component to a different node, add or remove dependencies between application components and/or nodes. 
     In response to detecting a change to the blueprint, graph layout manager  104  may modify structural information  116  of blueprint  126  to reflect the detected change. Graph layout manager  104  may insert a new entry into structural information  116  representing a newly added node, delete an entry from structural information  116  corresponding to a deleted node, insert or delete child elements into structural information  116  corresponding to changes of application components. In one embodiment, graph layout manager  104  may then recalculate positional information for nodes in the blueprint. For example, insertion of a new node may bump other nodes into new logical positions, while in other embodiments, deletion of an existing node may result in no change in other nodes&#39; logical position to improve visual stability and reduce GUI changes that are disorienting to the user. Graph layout manager  104  and SVG layout engine  106  may proceed to render blueprint  126  based on structural information  116 , as described above. In some embodiments, graph layout manager  104  and SVG layout engine  106  may clear out and completely re-render canvas  202  using the updated structural information. In other embodiments, graph layout manager  104  and SVG layout engine  106  may modify only those portions of the GUI affected by the change in structural information  116 . 
     The various embodiments described herein may employ various computer-implemented operations involving data stored in computer systems. For example, these operations may require physical manipulation of physical quantities usually, though not necessarily, these quantities may take the form of electrical or magnetic signals where they, or representations of them, are capable of being stored, transferred, combined, compared, or otherwise manipulated. Further, such manipulations are often referred to in terms, such as producing, identifying, determining, or comparing. Any operations described herein that form part of one or more embodiments of the invention may be useful machine operations. In addition, one or more embodiments of the invention also relate to a device or an apparatus for performing these operations. The apparatus may be specially constructed for specific required purposes, or it may be a general purpose computer selectively activated or configured by a computer program stored in the computer. In particular, various general purpose machines may be used with computer programs written in accordance with the teachings herein, or it may be more convenient to construct a more specialized apparatus to perform the required operations. 
     The various embodiments described herein may be practiced with other computer system configurations including hand-held devices, microprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers, and the like. 
     One or more embodiments of the present invention may be implemented as one or more computer programs or as one or more computer program modules embodied in one or more computer readable media. The term computer readable medium refers to any data storage device that can store data which can thereafter be input to a computer system computer readable media may be based on any existing or subsequently developed technology for embodying computer programs in a manner that enables them to be read by a computer. Examples of a computer readable medium include a hard drive, network attached storage (NAS), read-only memory, random-access memory (e.g., a flash memory device), a CD (Compact Discs) CD-ROM, a CD-R, or a CD-RW, a DVD (Digital Versatile Disc), a magnetic tape, and other optical and non-optical data storage devices. The computer readable medium can also be distributed over a network coupled computer system so that the computer readable code is stored and executed in a distributed fashion. 
     Although one or more embodiments of the present invention have been described in some detail for clarity of understanding, it will be apparent that certain changes and modifications may be made within the scope of the claims. Accordingly, the described embodiments are to be considered as illustrative and not restrictive, and the scope of the claims is not to be limited to details given herein, but may be modified within the scope and equivalents of the claims. In the claims, elements and/or steps do not imply any particular order of operation, unless explicitly stated in the claims. 
     Plural instances may be provided for components, operations or structures described herein as a single instance. Finally, boundaries between various components, operations and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of the invention(s). In general, structures and functionality presented as separate components in exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the appended claims(s).