Clarion/ASP: Code Generating ASP Business Applications

Transcription

1 Clarion/ASP: Code Generating ASP Business Applications June, 2002 Page 1

2 Contents Abstract... 3 Current State of ASP/ADO Development... 4 Overview: Clarion/ASP Development Details: Clarion/ASP Development Application Elements Conclusion June, 2002 Page 2

3 Abstract ASP is a web scripting architecture, which in combination with ADO (Active Data Objects) for database support, allows web designers to create browser based data centric applications. ASP is highly scalable and widely deployed. Clarion/ASP is a code generating tool for ASP applications which provide query, navigation and editing procedures for client/server databases over the web. It is geared for desktop developers or web designers who wish to automate the production of ASP applications through the use of re-usable code. It allows business application developers to easily translate behaviors normally found in line of business desktop applications to the web. Currently, ASP applications are usually the product of one-off development using a variety of hand coding techniques, simple wizards, and to a limited extent, code generating tools. The typical ASP developer may be a web designer, starting the development process using an HTML layout tool which provides wizards which creates starter code for the ADO data acess. ASP applications typically are limited in scope compared to desktop based business applications, and are more likely to be focused on a single data task than maintaining many tables. The Clarion/ASP finished product consists of ASP pages, HTML templates, and cascading style sheets. Business logic and user interface are completely separated, allowing developer or designer to work on one without affecting the other, protecting such customizations upon subsequent generations, and aiding the integration of Clarion/ASP procedures into existing sites both in looks and via links to and from existing pages of the site. June, 2002 Page 3

4 Current State of ASP/ADO Development ASP (Active Server Pages) is a scripting architecture developed by Microsoft for creating dynamic web pages. Its original use was for web site animations and transitions. The addition of ADO (Active Data Objects) to ASP allows for web based access to SQL client/ server databases via OLE DB (Object Linking and Embedding/ Database). Typical Use ASP/ADO provides excellent scalability, excellent compatibility with browsers, and in most cases, rapid access to data. As with other web scripting languages, the typical ASP/ADO developer is a web designer using a site layout tool who wishes to add database access to one or more pages at the site. The typical ASP/ADO application may be said, therefore, to focus on a single task, such as a simple table query, a lookup from a table, and perhaps an update to another table. Most such applications are one-off projects. Starting with a page layout, data access is subsequently either hand coded or created with June, 2002 Page 4

5 the help of a wizard which creates the base database access code, which is then refined by hand. In many cases, it is expected that the web designer, whose only function (most likely) is publishing web pages and applications, interacts with the DBA when creation or modification of a database structure such as a VIEW is necessary. Current ASP Development may thus be said to be characterized by: High Degree of Hand Coding/Customization for Each Project High Degree of Effort on Layout Little Reusability From Page to Page No Direct Interaction With Existing Repositories for Business Rules (such as those already kept in desktop development tools by the same enterprises deploying ASP applications). Little Cross Development Effort With Desktop Development Teams (the primary consumers of desktop development tools). June, 2002 Page 5

6 Web Server (IIS) Processes Script Initial Request Generates HTML Returns ResultSet Generates SQL Browser DBMS Deployment ASP and ADO technologies are widely deployed by virtue of being included in Windows NT Server and Windows 2000 Server. Commercial sites which utilize tools such as Microsoft Commerce Builder or SharePoint rely on ASP in combination with ADO to provide end user database access. Many other sites which depend on Microsoft for web server and/or database server software use ASP and ADO for data access. ADO usage is almost a given for MS SQL Server sites with a need to access data via the web. Development Tools Because the ASP applications themselves execute on the server and display inside most web browsers, deployment of the application to the client is in most cases not of concern to the developer. ASP Development tools are widespread, and stem from HTML layout and site deployment tools. June, 2002 Page 6

7 Such tools range from Microsoft Script Editor, which ships with MS Office, to Visual Studio.NET. Many non-microsoft environments such as C++ Builder also allow for generation of ASP code. There are many tools such as ColdFusion which provide data access via specialized HTML tags without the use of ASP. Within the Microsoft-centric segment of the web server universe, however, Visual InterDev (included in Visual Studio.NET) is the most widespread tool for creation of ASP/ADO applications. Visual InterDev relies upon layout tools and hand coding for its ASP support, and includes additional wizards to help include database access on a page by page basis. There are also third party tools which allow for page layout plus additional wizards to help include database access on a page by page basis. There are few ASP/ADO code generator tools outside of the wizards included in script layout tools. 1 Click DB Wizard Edition, from 1 Click DB Solutions, provides wizards which lay out entire pages and provide for navigation between browses (recordset tables), forms and queries. The ASP DataForm Wizard, specializes in generating form fill in access to SQL tables. Code Charge, from YesSoftware is a combination of wizards and a site-map like layout tool. Of these three products, it is the most comprehensive and produces an end result rivalling Clarion/ASP in breadth of the application procedures produced. It produces a variety of script target outputs. June, 2002 Page 7

8 Current Development Methodology Use of ADO access within ASP pages is generally a one-off process, in which a page provides access to a single table or stored procedure. This fits in with the approach to web development as a publishing process driven by designers rather than as a production/hosting environment for data access as designed and deployed by application developers. The look and feel of database forms or tabular data display must fit into the general design of the site. Using tools such as those described above, designers custom build data access pages. Many sites prefer to create parameterized stored procedures and simply display record sets to better fit data access functions to the tools used to create page layouts. Each page layout therefore requires either hand coding of ADO access or the use of a one time wizard, plus any additional DBMS based coding such as stored procedures. In these cases, most if not all data validation is performed at the DBMS. Yet even for these one-off page layout/data access tasks, there are common database functions such as logins, tabular data display, query, add, edit, delete. Business developers have long been familiar with client server tools which automate the production of forms for such functions. If these tasks could be automated, yet still offer the customization opportunities for their appearance which site designers demand, the productivity of the designers producing such pages would improve. June, 2002 Page 8

9 Current Business Database Access Use Desired Development Methodologies The ASP/ADO page-by-page development methodology described in the previous section is in sharp contrast with most client server business applications, which generally access several or more tables from a corporate database per application, in the form of lookups, drilldowns, etc. Though many desktop and Java Rapid Application Development environments support a procedural architecture which makes it possible for users to progress from query to form to lookup, and to traverse tables along relationships, this has been more difficult to achieve in ASP/ADO applications due to the stateless nature of the web. Part of this may be due to Microsoft s original recommendations to developers to limit the use of session variables, the easiest, most straightforward way to record status between page navigations, though that recommendation has been greatly relaxed recently. Such development environments, moreover, provide greater organization through improved project management, greater re-use of code from project to project, and sometimes via businessapplication-specific productivity aids such as database dictionaries which store business rules as kept by the DBMS. The number of web sites utilizing ASP for database access, the fact that such sites generally rely on one-off or hand coding for the production of ASP applications, and the fact that such sites generally may be said, by virtual of also developing Client Server desktop applications, to (at minimum) be aware of greater productivity in the development environments which produce these desktop applications indicates the following desired traits: June, 2002 Page 9

10 Accelerated development cycle: such sites are familiar with the benefits of rapid application development environments, and most likely produce in house desktop applications. Such sites could benefit from a similarly accelerated ASP application development cycle relying on reusable code, as used in desktop development in place of one-off wizards, hand coding, and individual design/layout customizations by page. Shared appearance with current site: in the same way that desktop applications by nature of their development tools integrate into the windows desktop, these sites would justifiably expect a similar integration into their existing web sites. Quality of finished product: the reusable components of desktop development environments are generally very advanced and reliable. Any ASP development tool considered as an analog for such tools should therefore be able to produce advanced and reliable ASP code. Implementation of business logic across multiple projects: this may be the current ASP development model s weakest point. Given the use of meta repositories in popular desktop development tools, expectations for a development environment for ASP would center on the storage of business rules defined within the DBMS or data dictionary and their use in multiple applications. Current ASP coding practice, via wizards and hand code, is unique to each project. ASP and Clarion/ASP Clarion/ASP may has been designed with the following goals: Accelerate development of ASP projects through the use of reusable ASP code. The ASP code is stored in Clarion templates. By interaction with the same data dictionary which also produces desktop applications, the Clarion development environment reads the dictionary symbols which represent the database, business rules and database structures and merges June, 2002 Page 10

11 them with the template ASP code according to options chosen by the developer through a design time template interface, outputting a mix of ASP and HTML pages accessing the database structures. Merge Database Access Into the Current Look of a Given Site: using a combination of customizable design time HTML templates (for general page setting ), run time HTML templates (for precise control layout), and standard cascading style sheets (for formatting), the ASP output may match the look of other pages at the site perfectly. Additionally, the web designer may add links to and from any part of the application (including individually specified data rows) and the rest of the site, exchanging field data via URL parameters and POST variables. Reliable, Modular, Useful Code: the generated code has been tested thoroughly and avoids common ASP coding mistakes such as returning null data. Common functions are kept small and stored in separate include files used by multiple pages. Extensive security checking, common database functions, etc. are built in. Integration with Business Rules Repository: the Clarion data dictionary queries the DBMS for a number of business rules. Once stored in the dictionary, upon generation the system implements client side validity checks in accordance with the business rules. Implementing the logic client side reduces communications between client, web server and DBMS and results in a more responsive system for the end user. Efficient Use of Programming and Design Resources: Clarion/ASP completely separates the business/application logic from the user interface. It stores the user interface into HTML templates which may be edited using standard HTML layout tools. This allows the web designer to provide for any desired customization of the look of the application with no effect on the application itself. Additionally, the application can June, 2002 Page 11

12 Generated Product later be modified without overwriting any customizations that the designer has already done. This allows a desktop application developer to work within the Clarion development environment to focus on the business/application logic, which is the developer s strength, and the designer to focus on the layout, which is the designer s strength, each collaborating on the overall design of the application. The ASP/ADO code generated by the application generator is highly compact and efficient, yet features robust error checking. The following provides a more detailed look: Processor Pages, which complement each of the.asp pages that Clarion/ASP generate for your procedures contain the database access code. The processors consist of small, tight loops which smoothly handle difficult access issues such as column names with embedded spaces, null values, which are particularly troublesome in.asp, and type conversions. Client side validation via compact Javascript functions. (see example message below): Customization support within the template interface which allows the developer at places to write their own HTML/ VBScript code to execute alongside the Clarion/ASP code June, 2002 Page 12

13 without harming the generated code, and without risk of overwriting the customizations at generation time. Rich support for displaying images, whether displayed from a database row or external file. A flexible security model which provides up to 99 security levels per procedure, along with options to allow viewing, adding, editing or deleting data according to the level of the user. (Template interface for defining the security table below): Automatic calls to login screens and user validation from within all pages using security, so that the proper security is in place even if the ASP page is called from a page not generated by Clarion/ASP. Extremely flexible interaction with URL parameters (and POST data), making it possible to identify record(s) for use when called from other pages at the site not generated by Clarion/ASP. Note: from the opposite direction, to POST data from the Clarion/ASP form to another form at the site not generated by Clarion/ASP, all naming conventions for Input elements are thoroughly documented, so that the web designer may receive their values on their own target page. Extremely flexible layouts via HTML run-time templates which allow layout modifications beyond the many options already available through the template interface. June, 2002 Page 13

14 A high degree of flexibility in appearance via use of style sheets that work along with the ASP pages allowing the developer and designer to define exactly the look desired, and which allow for the blending of the pages into an existing web with the same look and feel. The following charts a request for data (such as a single view-only form or navigable data table), as received from the client browser, using the authorization, access, and display logic generated by Clarion/ASP: Clarion/ASP Browser Client Data Request Browser Client Requests Information Results Returned to Client as a New Page Page Builder Checks for User Authorization Runs Authentication Routine and Returns Page Builder Loads HTML Template and Merges the Dynamic Data Page Builder Performs Data Access and Resolves Data Symbols Similarly, a request for an action (a submission by HTML for of an add, change, or delete), as received from the client browser, using June, 2002 Page 14

15 the authorization, access, and display logic generated by Clarion/ ASP can be charted as follows: Clarion/ASP Browser Client Form Action Request Browser Client Submits HTML Form Results Returned to Client as a New Page Processor Page Checks for User Authorization Runs Authentication Routine and Returns Processor Page Performs the Requested Data Update Processor Page Performs Data Validation Data Validation Error Error Message Returned to Client June, 2002 Page 15

16 Overview: Clarion/ASP Development Application Considerations The goal of the Clarion/ASP development process is to automate the process of creating attractive data-driven page layouts that integrate into existing webs, to apply the productivity expectations of modern business application development environments to the current hand coding/layout/wizard driven method of creating ASP/ADO applications, and to simulate some of the normal procedural flow of a desktop application via page to page navigation through data display, query forms, and input forms. Clarion/ASP application pages provide an application-like experience within the confines of the stateless browser experience. Clarion/ASP applications are by necessity always browser based applications, whose purpose is to query and display information quickly, and allow updates where permitted. In general these applications are for use with and SQL DBMS plus a separate web server. The following displays a framed based application showing a query page at left, and a browse table (navigable list) at right. June, 2002 Page 16

17 Because Clarion/ASP can quickly and easily generate pages for many procedures, each of which can add, insert, view or delete data from any table, as well as link to other procedures passing parameters as necessary, Clarion/ASP applications can be more readily adapted for use by business to extend the use of in house desktop applications to outside users. The most important concerns in this scenario are performance and security: In general, ASP/ADO applications can be fast and scale well, assuming that page design is not overloaded and hardware is appropriate. Clarion/ASP enhances performance via a small but sophisticated data validity checking library of java script functions which reduce communications between client, web server and DBMS by performing validity checks on the client. In addition, the ASP Processor page performs validation just prior to submission. Security of Microsoft Internet Information Servers, which are the exclusive hosts of ASP/ADO applications, have come into question recently. With proper application of hot fixes, the basic server security issues have been addressed. Application level security is provided in Clarion/ASP through an enhanced security model, in which user ID s and access levels are stored in a database table. Then, at two levels: entrance to each procedure, and access to individual table rows, Clarion/ASP generates code to present or not present procedures to the end user based upon their user ID and access level. June, 2002 Page 17

18 Clarion/ASP Generation Process The Clarion development system, at heart a code generation system, has always been envisioned to generate any type of database oriented code and has always been language independent. This product combines highly sophisticated template writing and highly sophisticated ASP coding, interacting with ADO to produce pages which mimic an equivalent procedure within a desktop application. The procedure, in fact, includes window controls and structures. The application generator analyzes the data-aware controls within a given window, creates HTML analogs for them, looks to the Clarion data dictionary for descriptions of the appropriate appearance and behavior for controls referencing the data, then creates ASP pages that process and the data, and merge these behaviors into a procedure-specific HTML template. Many customization options are available for each control, including the placement of custom controls which may provide links (dynamic or static, via text or graphic) to other procedures or pages, optionally passing data values for a given row/column as a parameter. The illustration below is of the properties for a custom control: June, 2002 Page 18

19 Also during the design process, the Clarion/ASP developer creates a style sheet which aids the process of integrating the Clarion/ASP pages into an existing site via appearance options. Another part of the design process allows for an underlying HTML template, upon which all the Clarion/ASP data can be displayed, in effect allowing the data to be merged into a standard page or frame background shared by other pages at the site. Customization and Deployment The end result is an ASP page that populates controls, calling processor pages (in the case of a form) which in turn control the row update. The developer working on Windows NT workstation, Windows 2000 Pro, or Windows XP Professional then tests on the local machine using IIS via the localhost IP address. After generation and testing of the pages, the Clarion/ASP developer may work with the web designer to further enhance the look of the page, make it work well with current site frames, prepopulate form data from other site forms or vice versa, and more. Clarion/ASP also supports a debug process, though one limited by the limitations imposed by a script based application. At that point the developer and web designer may deploy the pages. In case of major failure, such as inability to access the database, the Clarion/ASP code automatically s the web administrator. The illustration below displays an HTML frame at left, and a Clarion/ASP page at right: The end user has pressed a button which was automatically placed to the right of a data field. A popup calendar (javascript) appeared, ready for the end user to click a date, which will be returned to the date field. June, 2002 Page 19

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21 Details: Clarion/ASP Development Roadmap This section provides details of the development and deployment cycle for Clarion/ASP application pages. Detailing the actual steps summarized in the conceptual overview above, this section provides a simple overview of the development and execution of an application, from scratch. The developer starts with a Clarion database dictionary describing the structures in an SQL DBMS (hereafter, DBMS will refer to any client server relational Database Management System such as MS SQL Server, Oracle, IBM DB2, etc). The developer pre-formats the dictionary to include all relations, business rules, additional indices where a sort order request is expected, plain english descriptions for tables and fields, and control pre-formatting, as in the illustration below: The developer optionally adjusts the field order within each table as well as sets the do not populate options as June, 2002 Page 21

22 appropriate, in preparation for running the application wizard. Clarion/ASP, when applied, will read the list boxes (for browses) and entry controls (for forms) generated by the application wizard in order to determine which fields it should populate in its tables (for browses) and forms, in the order that the fields appear in those structures. The developer runs the application wizard (or creates an empty.app file and manually populates browse and form procedures). The developer applies the Clarion/ASP global extension template, specifying, at that time, the DSN, the HTML design time template, and the style sheet options, i.e., the global connectivity, look and feel options. The developer decides which procedures require ASP page equivalents. The developer applies the browse and form procedures respectively to the browses and forms in the application. The developer customizes the various fields within each procedure where necessary, using the design time interface, as in an example illustrated below. The developer links additional procedures as needed using the design time interface. (As an example, a navigational list view (browse) of a products table might link not only to the update form for the product, but also to a browse of all products by the supplier of the original product, and/or a June, 2002 Page 22

23 browse of all products in the same category as the selected product). The developer tests the various procedures locally using the Clarion/ASP generated menu page and a local copy of Internet Information Server. The developer fine tunes each procedure as necessary, whether for application logic, or look and feel. The developer generates the pages and tests them locally. The developer and web administrator together may optionally fine tune the generated pages. The developer and web administrator together provide links as needed, to/from the rest of the site to the ASP pages, and upload the ASP pages for deployment. June, 2002 Page 23

24 Application Elements This sections describes Clarion/ASP essential features and program elements. Security Clarion/ASP provides for a straightforward yet highly flexible security scheme based on a pyramid of user/group access rights with up to 99 user levels. When you enable security on a global level, each generated procedure will include a login routine. Access by the end user to any procedure page with security enabled will invoke a login screen. Once the user enters a successful login on one page, they may access any page their security level allows rights to, providing that any period of inactivity does not extend beyond a configurable timeout. If it does, they must log in again. You may designate a table within the database to store a user ID (we suggest that an address is highly useful for general public web applications), password, and access level (an integer between 1 and 99). Optionally, the table may store the user name (either first and last names separately, or first and last combined), and an address if not used for the user ID. The login messages/instructions are configurable, as in the illustration below: June, 2002 Page 24

25 After specifying that security is to be enabled, and designating the table which holds the user information, the developer may then set custom access levels by procedure (the default for all, once security is enabled, is 1). Within each procedure, the developer may separately specify separate access levels for viewing, editing, adding, and deleting data. Thus, should the developer specify that ordinary users are level 30, supervisors level 50, managers level 70 and senior managers level 90, a developer may specify that a particular form might be viewed by all, a new record added by supervisors and higher, an existing record edited by managers and higher, and deleted only by senior managers. With 99 possible values and four possible access levels per update form, the security system allows for many possible access scenarios. Login traffic between the browser and the server is unencrypted. My Records Security The purpose of My Records filtering is to limit the viewing and/ or editing of data to the owner (a single person or a group of users), as in the following examples: A column on any table can include a user ID (typically an address). Enabling the My Records filter on any procedure June, 2002 Page 25

26 referencing the table can therefore restrict access to any row that matches the user ID to the user ID with which the user logged in. Thus in a table of tasks, user one views only those tasks belonging to user one, and user two, only those belonging to user two. The Microsoft SQL Server Northwind sample database s employee table contains a reports to column. You may filter a browse which allows managers to see only their direct reports by specifying the reports to column as the data column to compare, and using the employee table as the security table, the employee ID as the user ID, and then using the UserID session variable to test against the reports to column. Similarly, you may declare an additional session variable, such as Department, edit the login.asp page to assign the session variable based upon department data which you would store in the security table, and then choose that session variable to compare to a department value in your primary browse table. You could similarly substitute region, sales territory, etc. Once you ve correctly set up the My Records options for each procedure, you need do no more; Clarion/ASP automatically hides the necessary fields, applies the necessary query filters, and takes care of setting the data defaults for new records. The illustration below shows the My Records field in a tasks table: Note that should you be applying the functionality to existing data and are adding a column to a table that you must add the values June, 2002 Page 26

27 necessary for the existing records, else they will not appear within any users My Records filter. Finally, note that you may place My Records on a form yet not place it on a browse, due to the fact that each procedure within Clarion/ASP is isolated from the other due to the nature of the web. This means that you may allow an end user to view all records within a browse, but restrict editing, deleting, or viewing details by placing the My Records filter on the form. User Interface Because the entire user interface is contained in HTML and CSS files separate from the application logic (contained in the ASP files), a web designer may customize the user interface in any standard HTML layout tool (and/or CSS editor) without affecting the application. The example below shows a runtime template being edited in an HTML layout tool. Note that the runtime colors and fonts are not visible because the layout tool doesn t display the formatting from the CSS file: June, 2002 Page 27

28 An application option allows subsequent regeneration of the project without overwriting the web designer s customizations, should it be necessary to change any of the application logic. Another key concept for developers used to creating desktop applications to understand when creating ASP applications is that HTML controls are different than Windows application controls. There is significantly less capability for customization and far less control over positioning. This leads us to a good news and bad news situation for desktop developers familiar with Clarion. The good news, despite these limitations, in Clarion/ASP we ve accomplished an extraordinary amount of mimicry of control formatting and layout using HTML 4.0 and stored it all in in the HTML page and style sheets for maximum flexibility. The bad news is that because there s no way to equate all the properties in the dictionary control formatting options with HTML we can t guarantee that everything will be perfect. For example, we can t provide for transparency, immediacy, selected coloring, or controlspecific cursors, to name a few. We can t recreate controls such as regions. Developers will find that your control formatting will be less visual, and more dependent on selecting properties from lists. Layouts are either horizontal, as in a browse, or vertical as in a form, one control to a line. You may specify the types of control, and a number of options for appearance and behavior, but it s not the same as designing a dialog box. Good use of style sheets, however, can make for a very attractive page. HTML Templates Though it may seem that everything is being called a template, Clarion templates and HTML templates are different things. This section focuses only on the HTML template. June, 2002 Page 28

29 When a user requests a page with data, the ASP code gathers the data and merges it into a standard HTML page. The merge target is called the runtime HTML template. The template is a normal HTML page, which contains a symbol for each piece of data which the merge function replaces with the actual data (either as text or a control) and formatting instructions (i.e., CSS style) during the merge process. In browse procedures, for example, you will find tokens in the occupying the table. Each token stands for the data which will replace the token. Should you wish to modify the layout, you may modify the HTML page. The runtime HTML template is a standard HTML file. The web designer can edit the runtime template with a standard HTML editor, moving and formatting the symbols as desired, without affecting the application. These HTML files are regenerated. The developer, however, may turn off HTML generation at the procedure level so as not to override the web designer s customizations. Cascading Style Sheets HTML style sheets, known as cascading style sheets (because one style may cascade its characteristics into another, and so forth), play a large role in many sites, and a large role in the Clarion/ASP pages. The style sheets declare classes, which consist solely of formatting instructions. You can then apply the style to a tag (be it a paragraph, cell in a table, a table, etc.), and that element will then be formatted according to the instructions in the style sheet. This allows any site to greatly change its look simply by substituting a new style sheet for an old one. Clarion/ASP allows you to define styles for elements such as table column headers, update form control labels (prompts), data rows, etc. You may then integrate an existing site style sheet with the one June, 2002 Page 29

30 Clarion/ASP produces or vice versa. You may also place references to both your Clarion/ASP produced style sheet and your corporate style sheet in each file, and the browser will merge the attributes of each when displaying the page to the end user. Browse The pages that Clarion/ASP creates have a look and feel almost entirely governed by style sheets and a base HTML template. The goal is that a developer can start with two things: a copy of a representative page from the web and the global style sheet for the site, and with them, quickly make the Clarion/ASP pages look like the rest of the site. This section describes the Clarion browse table, as implemented in Clarion/ASP. Purpose The browse presents an easy to use means to display and navigate tabular information. It presents the user with a page of data at a time (the number of rows for which are specified by the developer). The developer specifies a filter condition, which selects a subset of rows from the database. A navigation bar allows the end user to forward or reverse by a page, or jump to the end or back to the beginning. A query by form button allows the end user to select a subset of the subset by entering a sample value(s) for a field(s). A locator entry optionally allows the end user even quicker navigation, allowing them to type in a portion of data for a particular field, and then presenting the new subset immediately. Each row of data may June, 2002 Page 30

31 optionally allow for links to other browse tables or forms. For example, clicking on a company name may provide the end user with a detailed view of the company data. Similarly, each row may contain a link(s) leading to another browse(s), containing data from related tables, such as that company s products, or its orders, and so forth. In the illustration below, each row contains links to four related tables, plus, at far right, an automatically generated link to an update form for the row. Because the Clarion data dictionary is conversant with the table relations in the database, the developer may easily display a denormalized view of the data within the browse by specifying fields from multiple tables. Clarion/ASP automatically creates the proper JOIN statements for ADO access. Clarion/ASP also refers to the Clarion data dictionary for options to format the data on a field by field basis. In many cases, a Clarion browse allows the end user to proceed to an update form (or a view only form) by clicking on a data row. It takes only a small number of mouse clicks for the developer to implement this functionality. June, 2002 Page 31

32 Filtering Filtering the browse is accomplished through the where clause in the SQL query. It is, of course, also possible to create a view or stored procedure in the database to accomplish the same means. Clarion/ASP provides several levels of filtering opportunities. No filter at all. A view declared in the dictionary. A default where clause placed on the browse procedure properties. A called procedure placed on the browse procedure properties. A locator filter based upon text typed by the end user into a field associated with a specific column (as in where fieldname like ABC%). A Query by Form filter based upon example values typed into a form by the end user ID values: at the procedure level, the developer specifies a specific field may be identified to act as a URL parameter for a where clause value, as in URL?ID=value, where columname = value. Once the field is so identified, any linking page can pass the where clause value without even revealing the name of the field. The browse will then display. Clarion/ASP uses this method to pass data from procedure to procedure. In fact, Clarion/ASP can even pass a row value without displaying the value to the end user (for example, displaying a graphic instead). A specific where clause passed as a parameter from a linking page, via URL?WHR=clause. June, 2002 Page 32

33 A MyRecords filter, as described in the section on security, above. This is an important feature for sites which wish to manage user data in isolation from data belonging to other users. A combination of all the types of filters as described above. Links Links are the conduits through which one page leads to another on the Internet. There is no program flow like a desktop application. An important concept for database developers to grasp about ASP is that, like web pages, the browser and web server do not maintain a continuous connection. Further, the web server and the database do not maintain a continuous connection per each user. The only limitation on linking to a Clarion/ASP page is a logical one: if you wish to display a form containing only one record, or display a filtered browse, you must supply a way to identify the record(s) within the link. You can do this as a simple HTML parameter. The parameter will always be called ID. The field it refers to will be the unique ID field which you defined for the procedure extension. Optionally, a link from an outside page can pass a snippet of SQL which can then be appended to the WHERE clause. In Clarion/ ASP, this parameter is?whr. You may, for example, have a several links to a single browse. One link may have a parameter such as?whr=dbo.contacts.state=ny, another?whr=dbo.contacts.state=ca, etc. In each case, the same ASP page is the target, but each link returns different data (contacts from New York, contacts from California). June, 2002 Page 33

34 Conditional Formatting The browse procedure feature a rich array of conditional formatting options. The developer creates specific data row substyles in the style sheet for the project. Then, the developer may specify that the ASP applies styles according to: Provide a greenbar effect, applying two styles (usually the same text formatting, but with different background colors) to alternating rows. Greenbar formatting is the default, but can be overridden. Highlight specific rows which meet a test condition, such as the value in a particular column is equal to or greater than another value. Form Highlight specific grid cells, based upon a data value meeting a test condition. (This is the same as the second option, but applies the second style to a table cell instead of the entire row). The Clarion/ASP update form also provides for additions, deletions, and view only mode, in addition to allowing the end user to simply update the data. The update forms are actually four separate pages, one for each mode: add, delete, change, view. Each procedure may override security and style sheet preferences within an application, allowing you to make an update for a particular table different. The security options also allow you to specify which level of user access can call for each type of update. Appearance The default update form allows for a column of labels and a column of entry controls. The runtime HTML template is fully editable in most HTML layout tools. This allows the developer/ June, 2002 Page 34

35 designer to move data and column label tokens to wherever they wish. All formatting is applied via style sheets. In the example below, a view only update form contains a link (at bottom, not visible) to an editable update form. This link appears only when the end user has sufficient security rights. The updatable form would contain entry fields with the data (which appear only as text fields in this illustration). Selects Where a foreign key/primary key constraint between two tables specifies that a value in the child table must be present in the parent table, Clarion/ASP can place a list box containing those values in the update form. In fact, the list box may contain a completely different field in the related table, yet return the value corresponding to the proper field. This is important in working with normalized databases. An order form, for example, may contain a product ID number; yet it s much easier for the end user to choose by product name than by number. This is illustrated below. The end user selects Queso Cabrales from a dropdown June, 2002 Page 35

36 list, but the ASP page writes product number to the row when the end user presses the select button. Alternatively, the developer may choose that a popup window appear with a navigable table, so that when the end user clicks on a choice, the popup closes and the proper value is transferred to the edit box. This is the default because it is most suitable for cases in which the related table may have many rows. The select functionality is also provided for lists of items which may be entered in the dictionary directly, as opposed to existing within another table. Validity Checking An intelligent but compact Javascript function library allows for validity checking on the client side, reducing unnecessary network traffic. Functions may check data entry for numeric ranges, nulls, and more. When an error is encountered, Clarion/ASP automatically displays a message detailing the error so that the end user may correct the entry. Formatting functions are also applied both on read and write, allowing, for example, the limiting of a date entry in a field, even though the DBMS sees it as a date/time field. June, 2002 Page 36

37 Conclusion Clarion/ASP Provides a rich array of options for generating many ASP pages each of which corresponds to a common business application task such as querying a database, displaying rows of data from a table or view, and displaying and or editing a single row. The depth of automation in the process, the degree to which the resulting pages can be integrated into an existing site, and the level of customization offered to the web designer provide for superior productivity with a high degree of attractiveness in the end result. June, 2002 Page 37

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