[Letterhead of Theodore Goddard]



 The Dialog Corporation plc
 The Communications Building
 48 Leicester Square
 London
 WC2H 7DB

                                                            18 June 1999


 Dear Sirs,

 1             INTRODUCTION

 1.1           We are the solicitors to The Dialog Corporation plc (the
               "COMPANY") a public company incorporated with limited
               liability in England.

 1.2           We are writing to you with our opinion in connection with
               the filing with the Securities and Exchange Commission
               (the "COMMISSION") of the Company's Registration Statement
               on Form S-8 (the "REGISTRATION STATEMENT") under the
               Securities Act of 1933, as amended (the "SECURITIES ACT")
               relating to in aggregate 18,086,000 ordinary shares of 1
               pence each in the capital of the Company ("ORDINARY
               SHARES") which may be issued pursuant to the exercise of
               the following options granted or available to be granted
               over the following number of American Depositary Shares
               ("ADSs"):-

 1.2.1         6,250 ADSs issuable by the Company upon exercise of an
               option granted to Mr Roger Summit under a non-statutory
               stock option outside the Company's 1997 Share Option Plan
               (the "1997 PLAN") but subject to the terms and conditions
               of the 1997 Plan pursuant to an agreement dated 12 December
               1997 between the Company and Mr Roger Summit (the "SUMMIT
               AGREEMENT") and 6,250 ADSs issuable by the Company on
               exercise of an option granted to Mr Summit under a
               non-statutory stock option outside the 1997 Plan and dated
               1 April 1999 (the "SUMMIT OPTION");

 1.2.2         530,125 ADSs issuable by the Company upon the exercise of
               options granted pursuant to the 1997 Plan;

 1.2.3         67,720 ADSs issuable by the Company upon the exercise of
               options granted pursuant to the Company's 1998 Employee
               Stock Purchase Plan (the "1998 PLAN");

 1.2.4         6,711 ADSs issuable by the Company upon the exercise of an
               option granted pursuant to an option agreement between the
               Company (1) and Richard Swank (2) dated 14 November 1997
               and 4,232 ADSs issuable by the Company upon the exercise
               of an option granted pursuant to an option agreement
               between the Company (1) and Richard Swank (2) dated 8
               September 1998 (the "SWANK OPTION AGREEMENTS");

 1.2.5         3,900,212 ADSs relating to options or other rights to
               purchase available to be granted under the 1997 Plan and
               1998 Plan.

 1.3           The headings used in this letter are for ease of reference
               only.

 2             DOCUMENTS EXAMINED

 2.1           For the purpose of this opinion, we have examined the
               following copy documents provided by the Company:-

 2.1.1         the rules of the 1997 Plan as at the date hereof;

 2.1.2         the rules of the 1998 Plan as at the date hereof;

 2.1.3         the form of Purchase Plan Offering Document to be used in
               connection with the 1998 Plan (the "1998 PURCHASE PLAN
               OFFERING DOCUMENT");

 2.1.4         the Summit Agreement;

 2.1.5         the Summit Option;

 2.1.6         the Swank Option Agreements;

 2.1.7         minutes of a meeting of the board of directors of the
               Company passed on 13th November 1997 resolving, inter
               alia, to:

               (a)    adopt and approve the rules of the 1997 Plan;

               (b)    grant the following options pursuant to the 1997
                      Plan subject to closing of the acquisition pursuant
                      to a Stock Purchase Agreement dated 29 September
                      1997 between the Company and Knight - Ridder
                      Business Information Services, Inc. ("KR
                      INFORMATION ACQUISITION AGREEMENT");

                          NAME              NUMBER OF ADSs

                      Jeffery S Galt           25,000
                      Marck A Shipley          25,000
                      Peter Papano             12,500

               (c)    approve and grant an option to Richard Swank to
                      purchase ADSs pursuant to the Swank Option
                      Agreement dated 14 November 1997;

               (d)    authorise the Renumeration Committee to grant
                      options pursuant to the 1997 Plan;

 2.1.8         minutes of a meeting of the board of directors of the
               Company passed on 25 March 1998 and 25 June 1998 approving
               the rules of the 1998 Plan and the Purchase Plan Offering
               Document;

 2.1.9         notice of an extraordinary general meeting of the Company
               held on 10 November 1997  (the "EGM NOTICE");

 2.1.10        notice of an annual general meeting of the Company held on
               16 June 1998 (the "AGM NOTICE"):

 2.1.11        minutes of the Meeting referred to in paragraph 2.1.8
               above signed by Marmaduke Hussey recording that all of the
               resolutions referred to in the EGM Notice had been validly
               passed (the "EGM RESOLUTIONS") and a certified copy of the
               minutes of the meeting referred to in paragraph 2.1.9
               above certified by Jonathan Ball, the Company Secretary,
               recording that all of the resolutions referred to in the
               AGM Notice had been validly passed (the "AGM
               RESOLUTIONS");

 2.1.12        minutes of meetings of the Remuneration Committee of the
               Company held on:-

                      (a)  12 December 1997;
                      (b)  9 April 1998;
                      (c)  30 April 1998;
                      (d)  5 June 1998;
                      (e)  8 September 1998;
                      (f)  8 October 1998; and
                      (g)  1 April 1999;

 2.1.13        two sets of minutes of meetings of the board of directors
               of the Company each passed on 17 March 1999 ratifying the
               grant of options of the initial offering and the second
               offering under the 1998 Plan;

 2.1.14        board minutes of a meeting of the board of directors of
               the Company passed on 24 March 1999 ratifying execution of
               the Swank Option Agreement dated 8 September 1998 and
               approving the third offering under the 1998 Plan;

 2.1.15        resolutions of the remuneration committee of the board of
               directors of the Company dated on 1 April 1999; and

 2.1.16        a draft Registration Statement as set out in the Annexure
               attached to this letter.

 2.2           We have also examined a copy of the Memorandum and
               Articles of Association of the Company current at the date
               hereof.

 2.3           We have examined no other contracts, instruments or other
               documents entered into by or affecting the Company or any
               corporate records of the Company other than those
               specified in this paragraph 2 and paragraph 4 below and
               have not made any other enquiries concerning the Company.

 3             GENERAL ASSUMPTIONS AND CAVEATS

 3.1           In giving this opinion, we have assumed;

 3.1.1         each ADS represents four Ordinary Shares;

 3.1.2         the genuineness of all signatures;

 3.1.3         the conformity to original documents of all documents
               submitted to us as copies, the authenticity of all
               certifications of such copies and the authenticity and
               completeness of such original documents;

 3.1.4         the legal capacity of natural persons;

 3.1.5         the veracity, accuracy and completeness of all statements
               or opinions as to matters of fact made by an officer or
               officers of the Company (whether in writing or orally) to
               us and upon which we have relied without making any
               further enquiry in giving this opinion;

 3.1.6         that the resolutions of the board of directors of the
               Company referred to at paragraphs 2.1.7, 2.1.8, 2.1.12,
               2.1.13, 2.1.14 and 2.1.15 above were duly passed at
               properly convened and held meetings of such directors
               validly holding office and that duly qualified quorums of
               such directors voted in favour of such resolutions and
               that any provisions contained in the Companies Act 1985
               (as amended) (the "COMPANIES ACT") and/or the Company's
               Articles of Association relating to the declaration of
               directors' interests or the power of interested directors
               to vote were duly observed and that such resolutions have
               not been amended or rescinded and will at all times in the
               future remain in full force and effect;

 3.1.7         that the Memorandum and Articles of Association of the
               Company as referred to at paragraph 2.2 above have not
               been amended;

 3.1.8         that the provisions of the Shipley Agreement and the Swank
               Option Agreements and the options granted pursuant to the
               1997 Plan and the 1998 Plan constitute legally binding and
               enforceable obligations of the parties thereto under all
               applicable laws;

 3.1.9         that the EGM Resolutions were duly passed at a properly
               convened Extraordinary General Meeting of the Company on
               10 November 1997, that a quorum of members was present
               throughout the meeting and that the requisite majority
               voted in favour of approving the resolutions and that such
               resolutions have not been and will not be amended or
               rescinded and will remain at all times in the future in
               full force and effect;

 3.1.10        that the AGM Resolutions were duly passed at a properly
               convened Annual General Meeting of the Company on 16 June
               1998, that a quorum of members was present throughout the
               meeting and that the requisite majority voted in favour of
               approving the said resolutions and that such resolutions
               numbered 7, 8 and 9 in the AGM Notice have not been and
               will not be amended or rescinded at any time in the future
               and will remain at all times in the future in full force
               and effect;

 3.1.11        that no additional matters would have been disclosed by
               company searches of the file of the Company maintained by
               the Registrar of Companies (as defined in paragraph 4.1
               below) being carried out since the carrying out of the
               search referred to in paragraph 4.1 below;

 3.1.12        that the grant of options referred to in paragraphs 1.2.1
               to 1.2.4 (inclusive) have been and will at the date of
               issue of any Ordinary Shares pursuant to the exercise of
               the options referred to in those paragraphs be validly
               granted under the Plan or agreement (as the case may be)
               under which they are purported to be granted; and

 3.1.13        that the directors of the Company have approved the grant
               and the terms of the Summit Option.

 3.2           In giving this opinion we have also assumed that:-

 3.2.1         at the date of grant of the options referred to in
               paragraphs 1.2.1 to 1.2.4 (inclusive):-

               3.2.1.1   the Company had sufficient duly created and duly
                         authorised but unissued Ordinary Shares for the
                         options in question;

               3.2.1.2   the directors of the Company had the requisite
                         authority to grant those options and were
                         empowered to grant those options as if Section 89
                         of the Companies Act did not apply to any such
                         grant; and

               3.2.1.3  the directors of the Company or a duly authorised
                        Committee thereof passed the necessary resolutions
                        to grant these options.

 3.2.2         at the date of grant of any option or other rights
               referred to in paragraph 1.2.5 and at the date of issue of
               any of the Ordinary Shares pursuant to the exercise of
               options granted under the 1997 Plan and the 1998 Plan, the
               Swank Option Agreements and the Summit Agreement (together
               the "OPTION DOCUMENTS"):-

               3.2.2.1  the Company will have sufficient duly created and
                        duly authorised but unissued Ordinary Shares;

               3.2.2.2  the directors of the Company will have the
                        requisite authority to grant the options and allot
                        the Ordinary Shares and will be empowered to grant
                        such options and allot such Ordinary Shares as if
                        Section 89 of the Companies Act did not apply to
                        any such grant or allotment;

               3.2.2.3  options and other rights referred to in paragraph
                        1.2.5 will have been validly granted under the
                        1997 Plan and/or the 1998 Plan (as the case may
                        be);

               3.2.2.4  options referred to in paragraph 1.2 will be
                        validly exercised;

               3.2.2.5  such Ordinary Shares will be duly issued in
                        accordance with the relevant Option Document;

               3.2.2.6  the full subscription price payable for the issue
                        of such Ordinary Shares shall have been paid to
                        the Company in cleared funds;

               3.2.2.7  the directors of the Company or a duly authorised
                        Committee thereof will have passed and not amended
                        or revoked the necessary resolutions to grant the
                        relevant options and allot and issue such Ordinary
                        Shares;  and

               3.2.2.8  the resolutions referred to in paragraph 3.2.1.3
                        above will not have been amended or revoked;

 3.2.3         there will be no restrictions imposed otherwise than
               pursuant to the laws of England as at the date hereof or
               the current Memorandum and Articles of Association of the
               Company, affecting the ability of the Company to issue
               Ordinary Shares; and

 3.2.4         the Company will not have become insolvent, subject to
               liquidation or winding-up procedures, receivership or
               administration or struck-off the register or otherwise
               become subject to any legal disability to issue shares in
               the capital of the Company.

 Our opinion will not apply if the price payable for the issue of any
 Ordinary Share is less than the nominal value of such Ordinary Share.

 We have not taken any steps to verify any of the above assumptions.

 3.3           Apart from the knowledge of those members of this firm who
               have had the conduct of the preparation of this opinion,
               this opinion is not given on the basis of knowledge (if
               any) as to factual matters concerning the Company or any
               of its subsidiaries which may be possessed by any other
               member of this firm.

 3.4           We are qualified to practise in the laws of England and
               Wales only and we are not expert in, and we neither
               express nor imply any opinion as to, the laws of any
               jurisdiction other than the laws of England and Wales as
               applied by the courts of competent jurisdiction of England
               and Wales as at the date hereof.  In particular, but
               without limitation, we have made no investigation into the
               federal laws of the United States or the laws of any state
               in the United States (or of any political or judicial
               subdivision thereof) (as to which we express no opinion)
               nor do we give any opinion on the Company's ADSs or
               American Depositary Receipts referred to in any of the
               documents described in paragraph 2.1.

 3.5           We have made no investigation and express no opinion as to
               whether the Company has obtained all and any necessary
               consents, approvals or licences of any court or
               governmental agency of any applicable jurisdiction outside
               the United Kingdom of Great Britain and Northern Ireland
               (the "UNITED KINGDOM") for the performance of its
               obligations under the Option Documents;

 3.6           We have not investigated whether the Company is or will by
               reason of the matters contemplated by the Option Documents
               be in breach of any of its obligations under any
               agreement, document, deed or instrument except such
               documents as stated herein.

 3.7           We have not been involved in the drafting or preparation
               of the Registration Statement and therefore express no
               opinion as to the effectiveness of it to achieve the
               purposes contemplated by it.

 3.8           Our opinion is subject to the provisions of the Emergency
               Laws (Re-enactments and Repeals) Act 1964 (and directions
               issued by H.M. Treasury pursuant thereto) which contain
               certain restrictions in relation to securities held by
               residents of Iraq.

 4             SEARCHES AND ENQUIRIES

 4.1           We carried out on 7 June 1999 a search of the public
               file of the Company, being the file maintained in respect
               of the Company by the Registrar of Companies of England
               and Wales (the "REGISTRAR OF COMPANIES") in accordance
               with the Companies Act.  It should be noted that such file
               is not necessarily complete or up to date and we have not
               conducted any further search since such date.  We have
               examined and relied upon such of the records, documents,
               certificates and instruments as shown thereby as in our
               judgment are necessary or appropriate to enable us to give
               the opinions expressed in this letter.

 4.2           We have made no enquiry of the High Court of Justice in
               England and Wales (the "HIGH COURT") as to whether any
               petitions for winding-up or administration have been
               presented and are outstanding against the Company.  We
               have assumed for the purpose of this Opinion that no such
               petition has been presented, resolution passed or order or
               appointment made.

 4.3           We have carried out no other searches and enquiries other
               than that specified in paragraph 4.1.

 5             THE OPINION

 Based upon and relying upon, and subject to the foregoing, we are of the
 opinion that the Ordinary Shares to be issued pursuant to the exercise
 of options granted under the Option Documents will be validly issued and
 will be fully paid or credited as fully paid.

 6             CONFIDENTIALITY AND GOVERNING LAW

 6.1           We have acted for the Company alone and this opinion is
               for the use and benefit of the Company only in connection
               with filing of the Registration Statement with the
               Commission under the Securities Act.  It shall not be
               disclosed or communicated to any other party or relied on
               by any other party or for any other purpose or quoted or
               referred to in any public document, or filed with any
               governmental agency or other person without, in each such
               case, our prior written consent.

 6.2           We hereby consent to the filing of this opinion with the
               Commission as Exhibit 5.1 to the Registration Statement
               and to the use of our name in the Registration Statement
               in the form and context to which it appears in the
               Annexure.

 6.3           The terms of this opinion shall be governed by and
               construed in accordance with the laws of England.


 Yours faithfully,


 Theodore Goddard