OpenEMR System Architecture

OpenEMR System Architecture

Introduction

This is a compilation of notes that will be of interest to developers who wish to become involved with OpenEMR, or to users who are interested in technical aspects of the project. The initial creation of this document was generously sponsored by Sam Rajan, IPPF, and has since been updated by volunteer contributors.

Other Resources

Online Resources

The http://www.open-emr.org/ is the home page for the project, which includes a manual, demo site, forums and a documentation wiki.

Resources included within the OpenEMR package

• Current:
  • INSTALL provides installation and upgrading instructions
  • README provides a general description of OpenEMR
  • Documentation/Complete_Vaccine_Listing.pdf A standard listing of vaccinations.
  • de_identification_readme.txt Instructions for setting up de- identification of patient data.
  • Documentation/Emergency_User_README.txt Describes how to use the Emergency Login feature
  • Documentation/Payment_Posting_ZHH.pdf Description of how to use the billing module.
  • Documentation/README.phpgacl discusses phpGACL, which OpenEMR uses for access control.
  • Documentation/README-Log-Backup.txt How to set up a log rotation in OpenEMR.
  • Documentation/SystemArchitecture.txt provides a link to this wiki page.

• Somewhat Outdated:
  • Documentation/IPPF_Guides directory contains some nice visual documentation.
  • Documentation/User_Guide directory contains the OpenEMR 4.0 User Manual (HTML version). Note this is now considered outdated since OpenEMR 4.1+ and above maintain the User Manual on the wiki.

• Very Outdated:
  • Documentation/3rd_Party_Form_API.txt describes the interface as originally designed for encounter forms.(outdated)
  • Documentation/Database.pdf has some information about the original database design.(outdated)
  • Documentation/FAQ is also quite old and doesn't cover much.(outdated)
  • Documentation/Functions.pdf describes interfaces implemented by some modules in the library directory.(outdated)
  • Documentation/HISTORY.txt is a brief summary of OpenEMR versions thru about 2002.(outdated)
  • Documentation/modifications.txt is a brief list of the modules that must change in order to add data items to patient demographics.(outdated)
  • Documentation/NoIP.txt is an obsolete list of broken links.(outdated)
  • Documentation/OpenEMR_Backend_Spec.txt is a description of some interfaces implemented in the library directory.(outdated)
  • Documentation/OpenEMR-Win2003-server-install-new.html briefly discusses installation of OpenEMR on Windows 2003.(outdated)
  • Documentation/Package.txt has some old notes about creating an OpenEMR distribution release.(outdated)
  • Documentation/Readme.txt seems to be mostly a disclaimer regarding HIPAA compliance.(outdated)
  • accounting/README.sql-ledger which describes setup of SQL-Ledger with OpenEMR. (outdated)
  • Changelog which is not current.(outdated)

Customization of OpenEMR

• Most configuration happens within OpenEMR at Administration->Globals.
• If you code your encounters using methods other than CPT4, ICD9 and HCPCS then you will want to customize this at Administration->Lists->'Code Types' and also load your custom codes into the "codes" table.
• There are also configuration settings within OpenEMR at Administration->Files:
  • config.php
  • clickoptions.txt - May be customized to contain your preferred selections for issue titles (names of medical problems, allergies, etc.). Needs to be done concurrently with manual editing of the library/lists.inc file.
  • statement.inc.php - This is your template for patient statements or collection letters. It must be customized for your practice.
• custom/export_demographics.php - A placeholder for a script to export patient demographics to another system. export_labworks.php and export_xml.php are examples of such scripts.
• custom/refer.php - A placeholder for a referral management system. One option is to subscribe to refercare.org and then replace this script with the provided refercare.php script.
• interface/billing/billing_process.php - Customize X12 partner settings.
• library/lists.inc - Customize Issue Types.
• library/classes/class.ezpdf.php - Customize some general pdf settings.

Calendar Architecture

From some old notes when studying the PostNuke calendar design:

• openemr_postcalendar_events is referenced in:
  • interface/main/calendar/modules/PostCalendar/pnuser.php
  • interface/main/calendar/modules/PostCalendar/pnuserapi.php
  • interface/main/calendar/modules/PostCalendar/pninit.php
  • interface/main/calendar/modules/PostCalendar/common.api.php
  • interface/main/calendar/modules/PostCalendar/pntables.php
  • interface/main/calendar/modules/PostCalendar/pnadmin.php
  • interface/main/calendar/modules/PostCalendar/pnadminapi.php
  • interface/main/calendar/modules/PostCalendar/plugins/function.pc_filter.php
  • interface/reports/appt_encounter_report.php
• pnuser.php: function postcalendar_user_submit($args): invoked on event submission, at end writes success message, clears form vars, calls buildSubmitForm.
• common.api.php: function postcalendar_userapi_buildSubmitForm($args,$admin=false) creates a ton of output which is then written via the submit.html template.
• submit.html: is the template used to generate the redisplayed submit form.
• small_navigation.html: included to generate the date selector and view buttons.
• function.pc_date_select.php: builds date selector with jump button, should maybe enhance this to accept a specified default date, or else change the PostCalendar current working date from submit.html.
• function.pc_url.php: builds the urls for the links in the view buttons.

OpenEMR Dependencies

Ubuntu, Mint and Debian

This list of dependencies from installation of OpenEMR on Ubuntu, Mint and Debian may be helpful. These are the packages that were added to a basic installation. Installing these will also cause many other required dependencies to be installed:

• apache2
• mysql-server
• libapache2-mod-php5
• libdate-calc-perl
• libdbd-mysql-perl
• libdbi-perl
• libhtml-parser-perl
• libtiff-tools
• libwww-mechanize-perl
• libxml-parser-perl
• php5
• php5-mysql
• php5-cli
• php5-gd
• php5-xsl
• php5-curl
• php5-mcrypt
• php-soap
• imagemagick

Ubuntu 13.10

Need all in above ubuntu section including the following:

• php5-json

CentOS

Required modules:

• php
• php-cli
• php-common
• php-ldap
• php-mysql
• php-pdo
• php-soap
• php-xml

Redhat Enterprise 5 / CentOS 5

These are the rpm package names. "yum install <pkgname>" generally works.

• php-mysql
• php-gd

PHP Sessions and Browser Windows

Before August of 2007 OpenEMR worked poorly, even dangerously, when used in multiple top-level browser windows on the same machine. The underlying problem is that most web browsers cannot support separate cookie-based sessions in this case, because all windows share the same cookie storage area.

Then a JavaScript-based solution was implemented as follows:

1. interface/login/login.php was modified to delete the session cookie when a new login occurs. This ensures that a unique session ID is generated for each login (we assume you start each new browser window session with a login).
2. A JavaScript function restoreSession() was created via the script library/restoreSession.php. This script is included in every top-level window. When called, the function restores the session cookie's value to the session ID that was supplied when the window was created.
3. Many other scripts (about 200!) where changed to call "top.restoreSession()" wherever a server-side script is invoked. For example, "onclick='top.restoreSession()'" was added to every "<a href=...>" tag.

The effect of all this is to make the top-level window the storage area for the session cookie. So by creating multiple top-level browser windows and logging in separately to each, you can have multiple OpenEMR sessions concurrently on your desktop. This is a valuable feature for busy users who must juggle multiple tasks at once.

Naturally this impacts future development. You must include a JavaScript call to top.restoreSession() wherever you invoke a PHP script that requires current session data (which is most of them). The most common ways of doing this are by including the onclick handler as described above, and by including "onsubmit='return top.restoreSession()'" in <form> tags.