DOCSLIB.ORG

(EQL) – a Query Language for Archetype-Based Health Records

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
(EQL) – a Query Language for Archetype-Based Health Records MEDINFO 2007 K. Kuhn et al. (Eds) IOS Press, 2007 © 2007 The authors. All rights reserved. EHR Query Language (EQL) – A Query Language for Archetype-Based Health Records Chunlan Ma, Heath Frankel, Thomas Beale, Sam Heard Ocean Informatics Pty. Ltd, Australia Abstract data that end user needs [4]. EHR data include thousands of facts to do with a patient’s clinical status, which can be OpenEHR specifications have been developed to standard- highly structured, semi-structured or non-structured, or ise the representation of an international electronic health most commonly, a mixture of all three. The lack of disci- record (EHR). The language used for querying EHR data pline commonly found in EHR data not only increases the is not as yet part of the specification. To fill in this gap, difficulties in storing them, but particularly the difficulty Ocean Informatics has developed a query language cur- in querying them. rently known as EHR Query Language (EQL), a declarative language supporting queries on EHR data. The openEHR specifications have been developed to stan- EQL is neutral to EHR systems, programming languages dardise the representation of an international electronic and system environments and depends only on the health record (EHR)1. Although there are implementations openEHR archetype model and semantics. Thus, in princi- based on these specifications in development, experience ple, EQL can be used in any archetype-based with querying archetype-based EHR data is still limited, to computational context. In the EHR context described here, the point where it is not clear what kinds of query lan- particular queries mention concepts from the openEHR guage(s) are even appropriate for information systems EHR Reference Model (RM). EQL can be used as a com- based on archetypes. mon query language for disparate archetype-based Since the openEHR specifications intend to define a stan- applications. The use of a common RM, archetypes, and a dardised EHR infrastructure, a query language for this companion query language, such as EQL, semantic infrastructure should aim to become an open specification interoperability of EHR information is much closer. This as well. The query language described here will be submit- paper introduces the EQL syntax and provides example ted to the openEHR foundation as a candidate openEHR clinical queries to illustrate the syntax. Finally, current query language. implementations and future directions are outlined. There are four requirements for an archetype-based query Keywords: language. First, the query language should be able to openEHR reference model, archetype, query language, express queries for requesting any data item from an electronic health record archetype-based system, i.e. data defined in archetypes and/or the underlying reference model . Second, the query Introduction language should be able to be used by both domain profes- sionals and software developers. Third, the query language The National E-Health Transition Authority of Australia should be portable, i.e., be neutral to system implementa- (NEHTA) defines an EHR query as a formal user or sys- tion, application environment and programming language. tem request for information to the EHR repository/ Lastly, the syntax should be neutral with respect to the ref- database that specifies the constraints on precisely what erence model, i.e. the common data model of the part(s) of the EHR content needs to be retrieved [1]. Due to information being queried. Particular queries will of the lack of any clear standards in EHR query services, course be specific to a reference model. NEHTA has identified it as a major area for review [2]. The current available query languages that might poten- Easy accessibility of data from an electronic health record tially be used to query openEHR data include the XML (EHR) is considered as one of the essential features of the Query Language (XQuery) [5] and the Structured Query EHRs that can enhance a hospital revenue cycle [3]. There Language (SQL) . XQuery uses eXtensible Mark-up Lan- are two major challenges commonly encountered in clini- guage (XML) as its underlying data model. It has rich cal data accessibility: one is that people who understand predefined functions and allows user-defined functions the clinical data best, such as health professionals, are not supporting the kind of clinical data requests required in the the ones most competent of querying the data; another EHR context. It is platform independent. Nevertheless, its challenge is that qualified SQL programmers or other main strength is also its main flaw: it is limited to purely query language programmers must spend much time on exploring the data, composing tedious code to provide the 1 http://www.openehr.org/ 397 C. Ma et al. / EHR Query Language (EQL) – A Query Language for Archetype-Based Health Records XML data environments. Direct use of XQuery for the Object Query Language), and the study of the archetypes openEHR EHR would require that all openEHR data must technology, openEHR RM and openEHR path mecha- be represented in XML format. However, openEHR is nisms. designed as an object-oriented framework, and allows for a What is EQL multitude of data representations, including as program- ming language persistent objects (e.g. in the form of Java EQL is a declarative query language developed exclu- objects in a product such as db4o2); as language neutral sively for expressing the queries used for searching and objects (such as in a database like Matisse3); as relational retrieving the clinical data found in archetype-based structures (governed by an object/relational mapping EHRs. It is applied to the openEHR EHR Reference Model layer), and in various XML storage representations (e.g. (RM) and the openEHR clinical archetypes, but the syntax XML blob or XML databases). XQuery is therefore prob- is generic across applications, programming languages, lematic, because the query syntax is directly tied to the system environment, and reference model. The EQL is representational format of the data. Considerable efforts designed as a common language used for expressing clini- would be required to convert openEHR data in each cal data requests across multiple openEHR-based deployment context to XML just for the purpose of query- applications. ing; each such transformation may well be custom, The EQL has two innovations: 1) utilizing the openEHR requiring special work on the part of the system path mechanism to represent the query criteria and implementers. returned results; and 2) using a ‘containment’ mechanism A further disadvantage is that XQuery is a native XML to indicate the data hierarchy and constrain the source data programming language requiring intimate familiarity of to which the query is applied. both users (in this case, health professionals and software OpenEHR path mechanisms developers) alike with XML and XQuery, something that cannot be assumed. OpenEHR path syntax is used to locate clinical statements and data values within them using Archetypes. An Arche- SQL in its standard form is also not a viable candidate for type is a computable expression of a clinical concept in the querying archetype-based EHR data, because it does not form of structured constraint statements, based on some support object-structured data, e.g. the data modelled in reference model [7], such as the openEHR RM which pro- archetypes. It has been found that considerable intellectual vides the support for clinical archetypes. Each archetype efforts are required when using SQL to search and retrieve has a global unique identifier and each node of this arche- clinical data for both individual subject care and clinical type has a unique archetype node identifier. The openEHR research studies [6]. architecture has a path mechanism that enables any node Object Query Language (OQL) is a query language for within a top level structure to be specified from the top of object-oriented databases. OQL was developed by the the structure using a "semantic" X-path compatible path. Object Data Management Group (ODMG4), which was The availability of such paths radically changes the avail- disbanded in 2001. Comparing with XQuery and SQL, able querying possibilities with health information, and is OQL would be the best candidate query language used for one of the major distinguishing features of openEHR [8]. archetype-based EHR data. However, it is complex and as Consequently, it is possible to locate any node in an arche- a result, it has not been widely implemented. For large type, including leaf data elements by using the archetype object models, such as the openEHR RMs, OQL query and archetype node identifiers within openEHR paths. statements can become extremely verbose. OQL uses an Features of the EQL object programming style dot-notation to express object members, while an XPath-based syntax is specified by The EQL features are listed below: openEHR to locate archetype data elements. Using OQL • Neutral expression syntax. EQL does not have any with archetype-based EHRs would require the use and dependencies on the underlying RM of the archetypes. translation between these two notation styles. It is neutral to system implementation and environ- ment. This is one of the distinguishing features of the To satisfy the aforementioned requirements of an arche- EQL. type-based query language, a new language – EHR Query Language (EQL) is under development. This paper intro- • Allows setting query criteria using archetype and node duces the EQL features and syntax. Example clinical query identifiers, data values within the archetypes, and class scenarios are used to demonstrate the use of the EQL attributes defined within the openEHR RM. expression. • Allows the returned results to be top-level archetyped RM objects, data items within the archetypes or RM Methods attribute values. EQL was developed based on the analysis of a set of clini- • Supports naming returned results. cal query scenarios, the study of the current available • Support queries with logical time-based data rollback.
Load more

Recommended publications
  • CS145 Lecture Notes #15 Introduction to OQL
    CS145 Lecture Notes #15 Introduction to OQL History Object-oriented DBMS (OODBMS) vendors hoped to take market share from traditional relational DBMS (RDBMS) vendors by offer- ing object-based data management Extend OO languages (C++, SmallTalk) with support for persis- tent objects RDBMS vendors responded by adding object support to relational systems (i.e., ORDBMS) and largely kept their customers OODBMS vendors have survived in another market niche: software systems that need some of their data to be persistent (e.g., CAD) Recall: ODMG: Object Database Management Group ODL: Object De®nition Language OQL: Object Query Language Query-Related Features of ODL Example: a student can take many courses but may TA at most one interface Student (extent Students, key SID) { attribute integer SID; attribute string name; attribute integer age; attribute float GPA; relationship Set<Course> takeCourses inverse Course::students; relationship Course assistCourse inverse Course::TAs; }; interface Course (extent Courses, key CID) { attribute string CID; attribute string title; relationship Set<Student> students inverse Student::takeCourses; relationship Set<Student> TAs inverse Student::assistCourse; }; Jun Yang 1 CS145 Spring 1999 For every class we can declare an extent, which is used to refer to the current collection of all objects of that class We can also declare methods written in the host language Basic SELECT Statement in OQL Example: ®nd CID and title of the course assisted by Lisa SELECT s.assistCourse.CID, s.assistCourse.title FROM Students
    [Show full text]
  • EYEDB Object Query Language
    EYEDB Object Query Language Version 2.8.8 December 2007 Copyright c 1994-2008 SYSRA Published by SYSRA 30, avenue G´en´eral Leclerc 91330 Yerres - France home page: http://www.eyedb.org Contents 1 Introduction....................................... ............... 5 2 Principles ........................................ ............... 5 3 OQLvs.ODMG3OQL.................................... ........... 5 4 Language Concepts . ........... 7 5 Language Syntax . .......... 8 5.1 TerminalAtomSyntax.................................. .......... 8 5.2 Non Terminal Atom Production . 10 5.3 Keywords.......................................... 11 5.4 Comments.......................................... 11 5.5 Statements ........................................ 12 5.6 ExpressionStatements............................... 12 5.7 AtomicLiteralExpressions ............................ 14 5.8 ArithmeticExpressions ............................. 14 5.9 AssignmentExpressions .............................. 18 5.10 Auto Increment & Decrement Expressions . 19 5.11 Comparison Expressions . 20 5.12 Logical Expressions . 24 5.13 Conditional Expression . 24 5.14 ExpressionSequences ............................... 25 5.15 ArrayDeferencing ................................. 25 5.16 IdentifierExpressions .............................. 28 5.17 PathExpressions.................................... 32 5.18 FunctionCall....................................... 33 5.19 MethodInvocation................................... 34 5.20 Eval/Unval Operators . 37 5.21 SetExpressions...................................
    [Show full text]
  • SOQL and SOSL Reference
    SOQL and SOSL Reference Version 53.0, Winter ’22 @salesforcedocs Last updated: August 26, 2021 © Copyright 2000–2021 salesforce.com, inc. All rights reserved. Salesforce is a registered trademark of salesforce.com, inc., as are other names and marks. Other marks appearing herein may be trademarks of their respective owners. CONTENTS Chapter 1: Introduction to SOQL and SOSL . 1 Chapter 2: Salesforce Object Query Language (SOQL) . 3 Typographical Conventions in This Document . 5 Quoted String Escape Sequences . 5 Reserved Characters . 6 Alias Notation . 7 SOQL SELECT Syntax . 7 Condition Expression Syntax (WHERE Clause) . 9 fieldExpression Syntax . 13 USING SCOPE . 26 ORDER BY . 27 LIMIT . 28 OFFSET . 29 FIELDS() . 31 Update an Article’s Keyword Tracking with SOQL . 35 Update an Article Viewstat with SOQL . 35 WITH filteringExpression . 35 GROUP BY . 40 HAVING . 47 TYPEOF . 48 FORMAT () . 51 FOR VIEW . 51 FOR REFERENCE . 52 FOR UPDATE . 52 Aggregate Functions . 53 Date Functions . 58 Querying Currency Fields in Multi-Currency Orgs . 60 Example SELECT Clauses . 62 Relationship Queries . 63 Understanding Relationship Names . 64 Using Relationship Queries . 65 Understanding Relationship Names, Custom Objects, and Custom Fields . 66 Understanding Query Results . 68 Lookup Relationships and Outer Joins . 70 Identifying Parent and Child Relationships . 70 Understanding Relationship Fields and Polymorphic Fields . 72 Understanding Relationship Query Limitations . 77 Using Relationship Queries with History Objects . 77 Contents Using Relationship Queries with Data Category Selection Objects . 78 Using Relationship Queries with the Partner WSDL . 78 Change the Batch Size in Queries . 78 SOQL Limits on Objects . 79 SOQL with Big Objects . 83 Syndication Feed SOQL and Mapping Syntax .
    [Show full text]
  • Query Service Specification
    Query Service Specification Version 1.0 New Edition: April 2000 Copyright 1999, FUJITSU LIMITED Copyright 1999, INPRISE Corporation Copyright 1999, IONA Technologies PLC Copyright 1999, Objectivity Inc. Copyright 1991, 1992, 1995, 1996, 1999 Object Management Group, Inc. Copyright 1999, Oracle Corporation Copyright 1999, Persistence Software Inc. Copyright 1999, Secant Technologies Inc. Copyright 1999, Sun Microsystems Inc. The companies listed above have granted to the Object Management Group, Inc. (OMG) a nonexclusive, royalty-free, paid up, worldwide license to copy and distribute this document and to modify this document and distribute copies of the modified version. Each of the copyright holders listed above has agreed that no person shall be deemed to have infringed the copyright in the included material of any such copyright holder by reason of having used the specification set forth herein or having conformed any computer software to the specification. PATENT The attention of adopters is directed to the possibility that compliance with or adoption of OMG specifications may require use of an invention covered by patent rights. OMG shall not be responsible for identifying patents for which a license may be required by any OMG specification, or for conducting legal inquiries into the legal validity or scope of those patents that are brought to its attention. OMG specifications are prospective and advisory only. Prospective users are responsible for protecting themselves against liability for infringement of patents. NOTICE The information contained in this document is subject to change without notice. The material in this document details an Object Management Group specification in accordance with the license and notices set forth on this page.
    [Show full text]
  • Sciql, a Query Language for Science Applications
    SciQL, A Query Language for Science Applications M. Kersten, N. Nes, Y. Zhang, M. Ivanova CWI, Netherlands ABSTRACT technology has long been recognized [6, 34, 15, 18, 9, 20, 16, 4, Scientific applications are still poorly served by contemporary re- 31]. In particular, an efficient implementation of array and time lational database systems. At best, the system provides a bridge series concepts is missing [15, 34, 24, 1]. The main problems en- towards an external library using user-defined functions, explicit countered with relational systems in science can be summed up as import/export facilities or linked-in Java/C# interpreters. Time has (a) the impedance mismatch between query language and array ma- come to rectify this with SciQL1, a SQL-query language for science nipulation, (b) SQL is verbose for simple array expressions, (c) AR- applications with arrays as first class citizens. It provides a seam- RAYs are not first class citizens, (d) ingestion of Tera-bytes data is less symbiosis of array-, set-, and sequence- interpretation using too slow. The traditional DBMS simply carries too much overhead. a clear separation of the mathematical object from its underlying Moreover, much of the science processing involves use of standard storage representation. libraries, e.g., Linpack, and statistics tools, e.g., R. Their interac- The language extends value-based grouping in SQL with struc- tion with a database is often confined to a simplified import/export tural grouping, i.e., fixed-sized and unbounded groups based on dataset facility. A workflow management system is indispensable explicit relationships between its index attributes.
    [Show full text]
  • Object Persistence
    Object Persistence Object Oriented Programming Introduction • One of the most critical tasks that applications have to perform is to save and restore data • Persistence is the storage of data from working memory so that it can be restored when the application is run again • In object-oriented systems, there are several ways in which objects can be made persistent • The choice of persistence method is an important part of the design of an application Object Oriented Programming Object Serialization Object Oriented Programming Object Serialization • Simple persistence method which provides a program the ability to read or write a whole object to and from a stream of bytes • Allows Java objects to be encoded into a byte stream suitable for streaming to a file on disk or over a network • The class must implement the Serializable interface (java.io.Serializable), which does not declare any methods, and have accessors and mutators for its attributes Object Oriented Programming Object Serialization // create output stream File file = new File("teams_serialize.ser"); String fullPath = file.getAbsolutePath(); fos = new FileOutputStream(fullPath); // open output stream and store team t1 out = new ObjectOutputStream(fos); out.writeObject(t1); Object Oriented Programming Using Databases • Most Client-Server applications use a RDBMS as their data store while using an object-oriented programming language for development • Objects must be mapped to tables in the database and vice versa • Applications generally require the use of SQL statements embedded
    [Show full text]
  • Object Database Management Systems: Concepts and Features
    nIST Special Publication 500-179 Computer Systems Object Database Technology Management Systems: U.S. DEPARTMENT OF COMMERCE National Institute of Concepts and Features Standards and Technology Christopher E. Dabrowski Nisr Elizabeth N. Fong Deyuan Yang NAT L INST. OF STAND & TECH R.I.C, A111D3 3aTS7t, REFERENCE NIST PUBLICATIONS -QC" 100 U57 500-179 1990 NATIONAL MSTrrUTE OF STANDARDS & TECHNOLOGY Research Informatm Center Gaithersburg, MD 20899 NIST Special Publication 500-179 t Object Database Management Systems: Concepts and Features Christopher E. Dabrowski Elizabeth N. Fong Deyuan Yang National Computer Systems Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 April 1990 U.S. DEPARTMENT OF COMMERCE Robert A. Mosbacher, Secretary NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY John W. Lyons, Director Reports on Computer Systems Technology The National Institute of Standards and Technology (NIST) (formerly the National Bureau of Standards) has a unique responsibility for computer systems technology within the Federal government. NIST's National Computer Systems Laboratory (NCSL) develops standards and guidelines, provides technical assistance, and conducts research for computers and related telecommunications systems to achieve more effective utilization of Federal information technology resources. NCSL's responsibilities include development of technical, management, physical, and administrative standards and guidelines for the cost-effective security and privacy of sensitive unclassified information processed in Federal computers. NCSL assists agencies in developing security plans and in improving computer security awareness train- ing. This Special Publication 500 series reports NCSL research and guidelines to Federal agencies as well as to organizations in industry, government, and academia. National Institute of Standards and Technology Special Publication 500-179 Natl.
    [Show full text]
  • 1 Query Languages This Section Lists All the Query Languages That the Query Language Investigation Team Determined Were Relevant Possibilities
    1 Query Languages This section lists all the query languages that the Query Language Investigation team determined were relevant possibilities: 1.1 XPath Reference: http://www.w3.org/TR/xpath20/ 1.2 XQuery Reference: http://www.w3.org/XML/Query 1.3 XQL Reference: http://www.ibiblio.org/xql/xql-proposal.html 1.4 OQL Reference: http://www.odmg.org/ 1.5 SQL Reference: http://www.ansi.org/ 1.6 DMQL2 Reference: http://www.rets-wg.org/docs/index.html 2 XPath Query Language Comparison 2.1 XPath Language Definition XPath was designed to be used (by XSLT and XPointer) to address parts of an XML document either by location or by pattern matching capabilities exercised on content at those locations. Pattern matching is facilitated via string manipulation, numeric operations, and Boolean logic functionality. The language uses a compact, non-XML syntax that operates on the hierarchical structure of an XML document. Each XPath expression operates starting from the current context (a node within the document) and yields a node set, a boolean value, a number, or a string; expressions can be nested. The language consists of 37 tokens and 27 functions. 13 of the tokens are related to location, 14 to pattern matching, and 10 to the lexical structure. The functions deal with node identification, string manipulation, conversion to and numeric manipulation, and Boolean evaluation. Given that it operates on an XML document, to be used as the RETS query language between a client and a server XPath would require that the client and server share a common XML document representation of the data to be searched.
    [Show full text]
  • Apache Calcite for Enabling SQL Access to Nosql Data Systems Such As Apache Geode Christian Tzolov Whoami Christian Tzolov
    Apache Calcite for Enabling SQL Access to NoSQL Data Systems such as Apache Geode Christian Tzolov Whoami Christian Tzolov Engineer at Pivotal, Big-Data, Hadoop, Spring Cloud Dataflow, Apache Geode, Apache HAWQ, Apache Committer, Apache Crunch PMC member [email protected] blog.tzolov.net twitter: @christzolov https://nl.linkedin.com/in/tzolov Disclaimer This talk expresses my personal opinions. It is not read or approved by Pivotal and does not necessarily reflect the views and opinions of Pivotal nor does it constitute any official communication of Pivotal. Pivotal does not support any of the code shared here. 2 Big Data Landscape 2016 • Volume • Velocity • Varity • Scalability • Latency • Consistency vs. Availability (CAP) 3 Data Access • {Old | New} SQL • Custom APIs – Key / Value – Fluent APIs – REST APIs • {My} Query Language Unified Data Access? At What Cost? 4 SQL? • Apache Apex • SQL-Gremlin • Apache Drill … • Apache Flink • Apache Geode • Apache Hive • Apache Kylin • Apache Phoenix • Apache Samza • Apache Storm • Cascading • Qubole Quark 5 Geode Adapter - Overview SQL/JDBC/ODBC Parse SQL, converts into relational expression and Apache Calcite optimizes Push down the relational expressions supported by Geode Spring Data API for Enumerable OQL and falls back to the Calcite interacting with Geode Adapter Enumerable Adapter for the rest Convert SQL relational Spring Data Geode Adapter expressions into OQL queries Geode (Geode Client) Geode API and OQL Geode Server Geode Server Geode Server Data Data Data SQL Relational Expressions
    [Show full text]
  • ODL, OQL and SQL3 Object Definition Language
    ODL, OQL and SQL3 CSC 436 – Fall 2003 * Notes kindly borrowed from D R AZIZ AIT -BRAHAM, School of Computing, IS & Math, South Bank University 1 Object Definition Language oObjectives – Portability of database schemas across ODBMS – Interoperability of ODBMSs from multiple vendors oDevelopment principles – All semantic constructs of ODMG object model – Specification language (not full programming language) – Program language independence – OMG IDL (Interface Definition Language) compatibility – Practical and short time implementable 2 Type Specification oA type is defined by specifying its interface in ODL oTop-level BNF type definition ::= interface <type_name> [:<supertype_list>} { [<type_property_list>] [<property_list>] [<operation_list>] }; oAny list may be omitted if not applicable 3 Type Characteristics Specification oType characteristics – Supertypes – Extent naming – Key(s) oExample interface Professor :Person { extent professors; keys faculty_id, soc_sec_no; <property_list> <operation_list }; oNotes – No more than one extent or key definition. Each attribute or relationship traversal name in key definition should be specified in the property list – Extent naming and key definition may appear in any order – Supertype, extent naming and key definition may be omitted if not applicable 4 Property List oBNF <property_list ::== <property_spec>; | <property_spec><property_list> <property_spec>::= <attribute_spec> | <relationship_spec> oStructured types have bracketed list of field-type pairs associated with them. oEnumerated types
    [Show full text]
  • A Query Language for Analyzing Information Networks
    BiQL: a query language for analyzing information networks Anton Dries1,2, Siegfried Nijssen1 and Luc De Raedt1 1 Katholieke Universiteit Leuven, Belgium 2 Universitat Pompeu Fabra, Barcelona, Spain Abstract. One of the key steps in data analysis is the exploration of data. For traditional relational data, this process is facilitated by rela- tional database management systems and the aggregates and rankings they can compute. However, for the exploration of graph data, relational databases may not be most practical and scalable. Many tasks related to exploration of information networks involve computation and analy- sis of connections (e.g. paths) between concepts. Traditional relational databases o↵er no specific support for performing such tasks. For in- stance, a statistic such as the shortest path between two given nodes cannot be computed by a relational database. Surprisingly, tools for querying graph and network databases are much less well developed than for relational data, and only recently an increasing number of studies are devoted to graph or network databases. Our position is that the devel- opment of such graph databases is important both to make basic graph mining easier and to prepare data for more complex types of analysis. In this chapter, we present the BiQL data model for representing and manipulating information networks. The BiQL data model consists of two parts: a data model describing objects, link, domains and networks, and a query language describing basic network manipulations. The main focus here lies on data preparation and data analysis, and less on data mining or knowledge discovery tasks directly. 1 Introduction Information networks are a popular way of representing information.
    [Show full text]
  • 002.02 Comparing the Object and the Relational Data Model
    Paterson_656-0 C03.fm Page 31 Friday, March 31, 2006 3:50 PM CHAPTER 3 ■ ■ ■ Comparing the Object and Relational Data Models When people talk about databases, they almost always mean relational databases. This wasn’t always the case, though, as databases existed before the relational data model was developed. Now, the case for considering alternatives has become stronger with the increasing dominance of object-oriented languages in a widening range of application areas, and with the emergence of native object databases such as db4o. It’s vital to understand the benefits and limitations of today’s data models, particularly in the context of object-oriented systems. This chapter describes the evolution of data models, including the relational and the object-based “post-relational” models, and compares their characteristics, both good and bad. It discusses the strategies needed to make the relational model work with object-oriented systems. It then describes how object databases reflect the features expected in relational databases. The next chapter will examine the object data model in detail, and explain how this model is applied in db4o. Data Models Before the first DBMS was developed, programs accessed data from flat files. These did not allow representation of logical data relationships or enforcement of data integrity. Data modeling has developed over successive generations since the 1960s to provide applications with more powerful data storage features. In this chapter we will look at the differences between data models, concentrating on the relational model and the object model. Generally speaking, data models have evolved in three generations. The early generation data models tend to refuse to completely go away, however.
    [Show full text]